perf: Reduce memory copy when scanning from Python objects

[nameexhaustion]

Do this by making the backing memory an Arced trait object

[codecov]

Codecov Report

Attention: Patch coverage is 87.87879% with 4 lines in your changes missing coverage. Please review.

Project coverage is 79.56%. Comparing base (bcfa7ec) to head (64560d6).
Report is 39 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-python/src/file.rs	88.88%	2 Missing ⚠️
crates/polars-plan/src/plans/ir/scan_sources.rs	66.66%	1 Missing ⚠️
crates/polars-python/src/dataframe/io.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #20142      +/-   ##
==========================================
- Coverage   79.57%   79.56%   -0.02%     
==========================================
  Files        1563     1563              
  Lines      217395   217396       +1     
  Branches     2472     2472              
==========================================
- Hits       172986   172963      -23     
- Misses      43841    43865      +24     
  Partials      568      568              

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