feat: replace_children

[JSOD11]

Which issue does this PR close?

• Closes refactor(physical-plan): simplify ExecutionPlan children-replacement API #23441

Rationale for this change

What changes are included in this PR?

Are these changes tested?

Are there any user-facing changes?

[codecov-commenter]

Codecov Report

❌ Patch coverage is 81.08108% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.66%. Comparing base (88365dd) to head (1fdc7ab).
⚠️ Report is 7 commits behind head on main.

Files with missing lines	Patch %	Lines
...sion/physical-optimizer/src/hash_join_buffering.rs	41.66%	7 Missing ⚠️
datafusion/physical-plan/src/unnest.rs	86.95%	3 Missing ⚠️
...n/physical-plan/src/sorts/sort_preserving_merge.rs	90.00%	2 Missing ⚠️
...sion/physical-optimizer/src/output_requirements.rs	0.00%	0 Missing and 1 partial ⚠️
datafusion/physical-plan/src/execution_plan.rs	94.44%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #23903      +/-   ##
==========================================
+ Coverage   80.65%   80.66%   +0.01%     
==========================================
  Files        1093     1094       +1     
  Lines      371619   371806     +187     
  Branches   371619   371806     +187     
==========================================
+ Hits       299730   299922     +192     
+ Misses      53993    53980      -13     
- Partials    17896    17904       +8     

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