fix: Fix pickling polars.col on Python versions <3.11

[nameexhaustion]

Fixes #21021

This isn't an issue on Python >=3.11, but Python 3.10 EOL is still a bit far away at 2026-10, so I added this fix.

[codecov]

Codecov Report

Attention: Patch coverage is 16.66667% with 5 lines in your changes missing coverage. Please review.

Project coverage is 79.91%. Comparing base (de1d9d5) to head (4eec07f).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
py-polars/polars/functions/col.py	16.66%	4 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #21333      +/-   ##
==========================================
+ Coverage   79.85%   79.91%   +0.06%     
==========================================
  Files        1596     1596              
  Lines      228642   228648       +6     
  Branches     2615     2616       +1     
==========================================
+ Hits       182571   182732     +161     
+ Misses      45473    45317     -156     
- Partials      598      599       +1     

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