fix(python): Suggest str.contains for string containment in map_elements

[wtn]

Fixes #17182.

PolarsInefficientMapWarning incorrectly suggested .is_in() for string containment operations like substring in string inside map_elements.

Cause

Bytecode parser treated all in operations identically without checking operand types.

Fix

Use runtime type checking via _get_all_caller_variables() to distinguish:

• Collection literals/variables → .is_in()
• String literals/variables → .str.contains() with proper pl.lit() wrapping

[codecov]

Codecov Report

❌ Patch coverage is 39.13043% with 14 lines in your changes missing coverage. Please review.
✅ Project coverage is 79.89%. Comparing base (f83964f) to head (5cc6c66).
⚠️ Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
py-polars/src/polars/_utils/udfs.py	39.13%	10 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #25472      +/-   ##
==========================================
- Coverage   79.89%   79.89%   -0.01%     
==========================================
  Files        1781     1781              
  Lines      243417   243438      +21     
  Branches     3044     3050       +6     
==========================================
+ Hits       194475   194491      +16     
- Misses      48162    48165       +3     
- Partials      780      782       +2     

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[alexander-beedie]

Nice; when you think it's ready to roll, ping me and I'll review ;)

[wtn]

@alexander-beedie Ready for review. 🏓

[alexander-beedie]

@alexander-beedie Ready for review. 🏓

Nice; will take a look at the weekend :)