Fix EliminateLimit not eliminating limits under LogicalPlan::Extension nodes.

[masonh22]

Which issue does this PR close?

• Closes #.

Rationale for this change

#22298 updated the logical plan optimizer to apply optimization rules in place to avoid Arc unwrap/rewraps with a new map_children_mut() function. This function unconditionally updates the children of all logical plan nodes except for LogicalPlan::Extension nodes. For Extension nodes, it only updates the children if the mapping function returns true for any of the children, signifying that a child was updated.

When the EliminateLimit rule prunes a limit that has 0 skip and fetch, it modifies the node but does not return that it modified anything. This is fine for every case except for if the limit is underneath a LogicalPlan::Extension node, since it that case we ignore the output from the rule.

What changes are included in this PR?

This change adds a failing test, a fix to EliminateLimit, and changes map_children_mut() to unconditionally update the children of LogicalPlan::Extension nodes. The change to map_children_mut() could be left out, but I wouldn't be surprised if there are other optimization rules that modify the node without returning transformed=true, so this is done to avoid finding and fixing all of those cases.

What is the testing strategy for this PR?

I added a test that replicates the issue and fails without my fixes.

Are there any user-facing changes?

No

[codecov-commenter]

Codecov Report

❌ Patch coverage is 73.33333% with 4 lines in your changes missing coverage. Please review.
✅ Project coverage is 82.45%. Comparing base (0576a0b) to head (9fcc605).
⚠️ Report is 24 commits behind head on main.

Files with missing lines	Patch %	Lines
datafusion/optimizer/src/eliminate_limit.rs	78.57%	0 Missing and 3 partials ⚠️
datafusion/optimizer/src/optimizer.rs	0.00%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #25577      +/-   ##
==========================================
+ Coverage   82.42%   82.45%   +0.03%     
==========================================
  Files        1139     1140       +1     
  Lines      435372   436600    +1228     
  Branches   435372   436600    +1228     
==========================================
+ Hits       358845   360002    +1157     
- Misses      54826    54836      +10     
- Partials    21701    21762      +61     

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[alamb]

Makes sense to me -- thank you @masonh22

[alamb]

🧑‍🍳 👌