fix(rust): Allow read_csv schema to take unparsable types

[JamesCE2001]

Resolves #17349, also including support for pl.Time and pl.Categorical.

read_csv actually already supported passing these types to schema_overrides, but not to schema directly. This is mostly moving that to be shared functionally (which is the cause of the ugly diff in reader.rs) and fixing another bug I found in testing that prevented pl.Time from being read correctly.

[codecov]

Codecov Report

Attention: Patch coverage is 95.83333% with 2 lines in your changes missing coverage. Please review.

Project coverage is 80.50%. Comparing base (c537ba3) to head (8a50f88).
Report is 38 commits behind head on main.

Files	Patch %	Lines
crates/polars-io/src/csv/read/reader.rs	95.23%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #17765      +/-   ##
==========================================
- Coverage   80.50%   80.50%   -0.01%     
==========================================
  Files        1504     1504              
  Lines      197162   197140      -22     
  Branches     2806     2806              
==========================================
- Hits       158732   158703      -29     
- Misses      37909    37916       +7     
  Partials      521      521              

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[ritchie46]

Thanks @JamesCE2001. I've left a few comments.

[ritchie46]

Thanks @JamesCE2001