feat: Allow more join lossless casting

[ritchie46]

Also lossless cast expression that aren't only column references.

[codecov]

Codecov Report

Attention: Patch coverage is 97.50000% with 1 line in your changes missing coverage. Please review.

Project coverage is 78.98%. Comparing base (8b3afb7) to head (53cd222).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-plan/src/plans/conversion/join.rs	97.29%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #20474   +/-   ##
=======================================
  Coverage   78.98%   78.98%           
=======================================
  Files        1563     1563           
  Lines      220562   220570    +8     
  Branches     2490     2490           
=======================================
+ Hits       174206   174225   +19     
+ Misses      45783    45772   -11     
  Partials      573      573           

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