feat: Add FirstArgLossless supertype

[ritchie46]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 71.64179% with 19 lines in your changes missing coverage. Please review.

Project coverage is 78.95%. Comparing base (5f791b4) to head (fd295ed).
Report is 11 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-core/src/utils/supertype.rs	0.00%	9 Missing ⚠️
...ars-plan/src/plans/conversion/type_coercion/mod.rs	74.28%	9 Missing ⚠️
crates/polars-python/src/functions/misc.rs	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #20394      +/-   ##
==========================================
- Coverage   78.96%   78.95%   -0.01%     
==========================================
  Files        1561     1561              
  Lines      219871   219881      +10     
  Branches     2471     2471              
==========================================
- Hits       173611   173610       -1     
- Misses      45692    45703      +11     
  Partials      568      568              

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