chore: Make get_list_builder infallible

[ritchie46]

No description provided.

[codecov]

Codecov Report

Attention: Patch coverage is 97.43590% with 1 line in your changes missing coverage. Please review.

Project coverage is 79.67%. Comparing base (cca31b3) to head (e8e17a6).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
.../polars-core/src/chunked_array/builder/list/mod.rs	93.33%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #19217      +/-   ##
==========================================
- Coverage   79.68%   79.67%   -0.01%     
==========================================
  Files        1532     1532              
  Lines      209198   209200       +2     
  Branches     2417     2417              
==========================================
- Hits       166697   166680      -17     
- Misses      41953    41972      +19     
  Partials      548      548              

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