fix(python): Fix use of "hidden_columns" parameter in write_excel

[alexander-beedie]

Closes #18950.
Closes #18668.

A previous update caused the "hidden_columns" parameter to become inadvertently entangled with "column_widths" (for write_excel). This PR unentangles them, fixing the related issue(s) 😅

[codecov]

Codecov Report

Attention: Patch coverage is 75.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 79.87%. Comparing base (ab5200d) to head (b7a7f95).
Report is 72 commits behind head on main.

Files with missing lines	Patch %	Lines
py-polars/polars/dataframe/frame.py	75.00%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #19029      +/-   ##
==========================================
+ Coverage   79.85%   79.87%   +0.02%     
==========================================
  Files        1524     1524              
  Lines      207734   207750      +16     
  Branches     2908     2909       +1     
==========================================
+ Hits       165891   165946      +55     
+ Misses      41294    41254      -40     
- Partials      549      550       +1     

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