fix: Respect user passed 'reader_schema' in 'scan_csv'

[ritchie46]

fixes #15254

[codecov]

Codecov Report

Attention: Patch coverage is 85.36585% with 6 lines in your changes are missing coverage. Please review.

Project coverage is 80.97%. Comparing base (575e917) to head (d6550c3).

Files	Patch %	Lines
...s-lazy/src/physical_plan/executors/scan/parquet.rs	60.00%	6 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16080      +/-   ##
==========================================
- Coverage   80.97%   80.97%   -0.01%     
==========================================
  Files        1386     1386              
  Lines      178439   178465      +26     
  Branches     3075     3075              
==========================================
+ Hits       144497   144513      +16     
- Misses      33451    33461      +10     
  Partials      491      491              

Flag	Coverage Δ
python	74.53% <85.36%> (-0.01%)	⬇️
rust	78.13% <85.36%> (-0.01%)	⬇️

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