refactor: Implement Hash and use SpecialEq for RenameAliasFn

[JakubValtar]

A touch-up for #22988

[codecov]

Codecov Report

Attention: Patch coverage is 30.00000% with 7 lines in your changes missing coverage. Please review.

Project coverage is 80.36%. Comparing base (baf06d8) to head (5e1943b).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-plan/src/dsl/expr/mod.rs	33.33%	4 Missing ⚠️
crates/polars-plan/src/dsl/expr/expr_dyn_fn.rs	0.00%	3 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #22989      +/-   ##
==========================================
- Coverage   80.37%   80.36%   -0.02%     
==========================================
  Files        1682     1682              
  Lines      223209   223211       +2     
  Branches     2804     2804              
==========================================
- Hits       179401   179380      -21     
- Misses      43139    43162      +23     
  Partials      669      669              

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