Improve performance of CBOR serialization and deserialization, and fix negative timestamps

[ashovlin]

Issue #, if available: N/A

Description of changes:

1. Implements some performance optimizations for the CBOR serializer and deserializer. Most of this was hoisting constants that were defined in each method up to the class level. It also reworks _serialize_data_item with if/elif instead of building the method name dynamically and simplified some hot paths.
2. While here, found a bug in serializing pre-epoch timestamps.

I still need to run the internal benchmarks on the standard instances, but results locally:

================================================================================
  rpcv2Cbor_GetItemOutputBinary_L
================================================================================
  metric           before        after         diff   % change
  ----------------------------------------------------------
  mean             305627       255278       -50349     -16.5%
  p50              299666       253667       -45999     -15.4%
  p90              322416       259792       -62624     -19.4%
  p95              331208       264833       -66375     -20.0%
  p99              350250       279125       -71125     -20.3%
  std_dev           12964         6285        -6679     -51.5%

================================================================================
  rpcv2Cbor_GetItemOutputBinary_M
================================================================================
  metric           before        after         diff   % change
  ----------------------------------------------------------
  mean              49255        41777        -7478     -15.2%
  p50               47958        41250        -6708     -14.0%
  p90               53125        42166       -10959     -20.6%
  p95               56875        45583       -11292     -19.9%
  p99               62542        51333       -11209     -17.9%
  std_dev            5600         2384        -3216     -57.4%

================================================================================
  rpcv2Cbor_GetItemOutputBinary_S
================================================================================
  metric           before        after         diff   % change
  ----------------------------------------------------------
  mean              15613        13953        -1660     -10.6%
  p50               15292        13666        -1626     -10.6%
  p90               15875        14250        -1625     -10.2%
  p95               16833        15333        -1500      -8.9%
  p99               19917        18208        -1709      -8.6%
  std_dev            3057         1871        -1186     -38.8%

================================================================================
  rpcv2Cbor_GetItemOutput_Baseline
================================================================================
  metric           before        after         diff   % change
  ----------------------------------------------------------
  mean               2618         2660          +42      +1.6%
  p50                2459         2583         +124      +5.0%
  p90                2667         2667            0      +0.0%
  p95                3167         2750         -417     -13.2%
  p99                3625         3458         -167      -4.6%
  std_dev            1515         1278         -237     -15.6%

================================================================================
  rpcv2Cbor_GetItemOutput_L
================================================================================
  metric           before        after         diff   % change
  ----------------------------------------------------------
  mean             310398       266950       -43448     -14.0%
  p50              306292       255458       -50834     -16.6%
  p90              324583       264334       -60249     -18.6%
  p95              337042       273291       -63751     -18.9%
  p99              353542       674042      +320500     +90.7%
  std_dev           11485        81964       +70479    +613.7%

================================================================================
  rpcv2Cbor_GetItemOutput_M
================================================================================
  metric           before        after         diff   % change
  ----------------------------------------------------------
  mean              49209        42415        -6794     -13.8%
  p50               48541        41667        -6874     -14.2%
  p90               50625        43834        -6791     -13.4%
  p95               54083        47041        -7042     -13.0%
  p99               58792        52959        -5833      -9.9%
  std_dev            2891         4506        +1615     +55.9%

================================================================================
  rpcv2Cbor_GetItemOutput_S
================================================================================
  metric           before        after         diff   % change
  ----------------------------------------------------------
  mean              16124        16186          +62      +0.4%
  p50               15792        14792        -1000      -6.3%
  p90               16500        20042        +3542     +21.5%
  p95               18250        20709        +2459     +13.5%
  p99               20709        22833        +2124     +10.3%
  std_dev            1559         4182        +2623    +168.2%

================================================================================
  rpcv2Cbor_PutItemRequest_Baseline
================================================================================
  metric           before        after         diff   % change
  ----------------------------------------------------------
  mean               6137         3537        -2600     -42.4%
  p50                4083         3250         -833     -20.4%
  p90                5375         3583        -1792     -33.3%
  p95               12167         4208        -7959     -65.4%
  p99               51792         4500       -47292     -91.3%
  std_dev           14235         4241        -9994     -70.2%

================================================================================
  rpcv2Cbor_PutItemRequest_BinaryData_L
================================================================================
  metric           before        after         diff   % change
  ----------------------------------------------------------
  mean              58037        50209        -7828     -13.5%
  p50               55834        48875        -6959     -12.5%
  p90               63583        53959        -9624     -15.1%
  p95               67125        56583       -10542     -15.7%
  p99               90542        62000       -28542     -31.5%
  std_dev            9128         4413        -4715     -51.7%

================================================================================
  rpcv2Cbor_PutItemRequest_BinaryData_M
================================================================================
  metric           before        after         diff   % change
  ----------------------------------------------------------
  mean              20601        16817        -3784     -18.4%
  p50               19750        16375        -3375     -17.1%
  p90               23833        17292        -6541     -27.4%
  p95               25000        19209        -5791     -23.2%
  p99               26209        21583        -4626     -17.7%
  std_dev            3888         3132         -756     -19.4%

================================================================================
  rpcv2Cbor_PutItemRequest_BinaryData_S
================================================================================
  metric           before        after         diff   % change
  ----------------------------------------------------------
  mean               5306         4325         -981     -18.5%
  p50                5166         4250         -916     -17.7%
  p90                5875         4334        -1541     -26.2%
  p95                6625         4375        -2250     -34.0%
  p99                6875         5500        -1375     -20.0%
  std_dev            1130         1101          -29      -2.6%

================================================================================
  rpcv2Cbor_PutItemRequest_MixedItem_L
================================================================================
  metric           before        after         diff   % change
  ----------------------------------------------------------
  mean             276349       217368       -58981     -21.3%
  p50              272875       213958       -58917     -21.6%
  p90              285708       228375       -57333     -20.1%
  p95              294291       235000       -59291     -20.1%
  p99              315792       246625       -69167     -21.9%
  std_dev           11152         9199        -1953     -17.5%

================================================================================
  rpcv2Cbor_PutItemRequest_MixedItem_M
================================================================================
  metric           before        after         diff   % change
  ----------------------------------------------------------
  mean              92333        75228       -17105     -18.5%
  p50               91375        72875       -18500     -20.2%
  p90               94583        81458       -13125     -13.9%
  p95               98333        84083       -14250     -14.5%
  p99              106250        93208       -13042     -12.3%
  std_dev            4642         6282        +1640     +35.3%

================================================================================
  rpcv2Cbor_PutItemRequest_MixedItem_S
================================================================================
  metric           before        after         diff   % change
  ----------------------------------------------------------
  mean              18225        14989        -3236     -17.8%
  p50               17750        14375        -3375     -19.0%
  p90               18708        16750        -1958     -10.5%
  p95               19625        18000        -1625      -8.3%
  p99               23625        19083        -4542     -19.2%
  std_dev            3626         3684          +58      +1.6%

================================================================================
  rpcv2Cbor_PutItemRequest_Nested_L
================================================================================
  metric           before        after         diff   % change
  ----------------------------------------------------------
  mean              47264        47034         -230      -0.5%
  p50               45917        39333        -6584     -14.3%
  p90               50458        59834        +9376     +18.6%
  p95               53750        92458       +38708     +72.0%
  p99               61083       134750       +73667    +120.6%
  std_dev            9601        28468       +18867    +196.5%

================================================================================
  rpcv2Cbor_PutItemRequest_Nested_M
================================================================================
  metric           before        after         diff   % change
  ----------------------------------------------------------
  mean              12218         9980        -2238     -18.3%
  p50               11625         9500        -2125     -18.3%
  p90               13250        11291        -1959     -14.8%
  p95               14875        12041        -2834     -19.1%
  p99               16208        12625        -3583     -22.1%
  std_dev            3916         3498         -418     -10.7%

================================================================================
  rpcv2Cbor_PutItemRequest_ShallowMap_L
================================================================================
  metric           before        after         diff   % change
  ----------------------------------------------------------
  mean             342857       254479       -88378     -25.8%
  p50              336708       251500       -85208     -25.3%
  p90              372459       263167      -109292     -29.3%
  p95              380083       269959      -110124     -29.0%
  p99              455292       284500      -170792     -37.5%
  std_dev           34236         8205       -26031     -76.0%

================================================================================
  rpcv2Cbor_PutItemRequest_ShallowMap_M
================================================================================
  metric           before        after         diff   % change
  ----------------------------------------------------------
  mean             113269        80618       -32651     -28.8%
  p50              109250        79833       -29417     -26.9%
  p90              114083        82833       -31250     -27.4%
  p95              123542        86333       -37209     -30.1%
  p99              202750        93583      -109167     -53.8%
  std_dev           30515         2821       -27694     -90.8%

================================================================================
  rpcv2Cbor_PutItemRequest_ShallowMap_S
================================================================================
  metric           before        after         diff   % change
  ----------------------------------------------------------
  mean              22764        13172        -9592     -42.1%
  p50               17250        13041        -4209     -24.4%
  p90               22541        13292        -9249     -41.0%
  p95               44417        13625       -30792     -69.3%
  p99              156708        16750      -139958     -89.3%
  std_dev           31672         1034       -30638     -96.7%

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[ashovlin]

#10644 is adding the timestamp fix and will likely merge first