fix: Only rewrite numeric ineq joins

[ritchie46]

fixes #19080

[codecov]

Codecov Report

Attention: Patch coverage is 92.30769% with 2 lines in your changes missing coverage. Please review.

Project coverage is 79.77%. Comparing base (35946cf) to head (e086a99).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-plan/src/plans/conversion/join.rs	90.90%	1 Missing ⚠️
.../polars-plan/src/plans/optimizer/collapse_joins.rs	93.33%	1 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #19083   +/-   ##
=======================================
  Coverage   79.76%   79.77%           
=======================================
  Files        1531     1531           
  Lines      208521   208545   +24     
  Branches     2913     2913           
=======================================
+ Hits       166332   166365   +33     
+ Misses      41638    41629    -9     
  Partials      551      551           

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