fix(python): Raise for overlapping index/column names in pandas dataframes post string coercion

[tylerriccio33]

Hi Polars team, this pr does 3 main things. First, it solves for #15938 and #16023 , by checking the stringified index names for overlap w/column names. Second, it solves for duplicated index names, post string conversion. For example, an index of 0 and '0' would not be caught without this explicit check. Third, I combine this logic with the code I wrote for issue #16025 , because I considered this all a part of the same general problem.

I altered some unit tests to include the new error message, two of which I already altered for my pr on #16025 . I wrote/borrowed a new unit test that was written directly from the desired behavior in #15938 .

Let me know if you need anything else. I'd love for any feedback on the code, if there's anything you'd change.

Thank you.

[codecov]

Codecov Report

Attention: Patch coverage is 76.92308% with 3 lines in your changes missing coverage. Please review.

Project coverage is 80.69%. Comparing base (b85654e) to head (e1911c1).

Files	Patch %	Lines
py-polars/polars/_utils/construction/dataframe.py	76.92%	2 Missing and 1 partial ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main   #17628   +/-   ##
=======================================
  Coverage   80.69%   80.69%           
=======================================
  Files        1484     1484           
  Lines      195409   195418    +9     
  Branches     2779     2780    +1     
=======================================
+ Hits       157679   157692   +13     
+ Misses      37220    37215    -5     
- Partials      510      511    +1     

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[ritchie46]

Seems good. Thanks!