Fix self join leaf expressions

[cetra3]

Which issue does this PR close?

• Closes push_down_leaf_projections fails for self joins in some scenarios #24241

Rationale for this change

This is a bugfix for a specific query shape.

What changes are included in this PR?

Changes the way leaf expressions are extracted when the alias is essentially the same as the column

Are these changes tested?

Yes, with a test that fails on main currently

Are there any user-facing changes?

Nope

[codecov-commenter]

Codecov Report

❌ Patch coverage is 78.04878% with 9 lines in your changes missing coverage. Please review.
✅ Project coverage is 80.98%. Comparing base (a9b61ab) to head (d935290).

Files with missing lines	Patch %	Lines
...tafusion/optimizer/src/extract_leaf_expressions.rs	78.04%	0 Missing and 9 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #24242      +/-   ##
==========================================
- Coverage   80.99%   80.98%   -0.01%     
==========================================
  Files        1106     1106              
  Lines      383549   383590      +41     
  Branches   383549   383590      +41     
==========================================
+ Hits       310644   310664      +20     
- Misses      54570    54578       +8     
- Partials    18335    18348      +13     

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