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 79.64%. Comparing base (8ab1657) to head (fa6da50).

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   79.58%   79.64%   +0.06%     
==========================================
  Files        1743     1743              
  Lines      240439   240460      +21     
  Branches     3038     3044       +6     
==========================================
+ Hits       191347   191517     +170     
+ Misses      48310    48159     -151     
- Partials      782      784       +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 :)

[alexander-beedie]

Umm... THIS weekend 😄