refactor(python): Organize utils for I/O functionality

[stinodego]

Just some light refactoring.

[codecov]

Codecov Report

Attention: Patch coverage is 94.25287% with 5 lines in your changes are missing coverage. Please review.

Project coverage is 81.16%. Comparing base (49e4244) to head (42b5b1f).

Files	Patch %	Lines
py-polars/polars/io/spreadsheet/functions.py	50.00%	1 Missing and 1 partial ⚠️
py-polars/polars/io/parquet/anonymous_scan.py	50.00%	0 Missing and 1 partial ⚠️
py-polars/polars/io/parquet/functions.py	75.00%	0 Missing and 1 partial ⚠️
py-polars/polars/io/spreadsheet/_utils.py	92.85%	0 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15529      +/-   ##
==========================================
- Coverage   81.16%   81.16%   -0.01%     
==========================================
  Files        1362     1363       +1     
  Lines      175001   175009       +8     
  Branches     2532     2532              
==========================================
+ Hits       142037   142040       +3     
- Misses      32481    32487       +6     
+ Partials      483      482       -1     

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