chore: Add AExpr::is_expr_equal_to

[coastalwhite]

ping @JakubValtar

[codecov]

Codecov Report

Attention: Patch coverage is 0% with 115 lines in your changes missing coverage. Please review.

Project coverage is 81.30%. Comparing base (226a8a2) to head (2e4dfbd).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-plan/src/plans/aexpr/equality.rs	0.00%	66 Missing ⚠️
crates/polars-plan/src/plans/aexpr/traverse.rs	0.00%	49 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #23740      +/-   ##
==========================================
- Coverage   81.33%   81.30%   -0.04%     
==========================================
  Files        1650     1651       +1     
  Lines      224103   224230     +127     
  Branches     2851     2851              
==========================================
+ Hits       182283   182312      +29     
- Misses      41111    41209      +98     
  Partials      709      709              

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