refactor(rust): Reorganize polars_io::parquet module

[stinodego]

Similar to #15831

[codecov]

Codecov Report

Attention: Patch coverage is 89.35484% with 33 lines in your changes are missing coverage. Please review.

Project coverage is 81.37%. Comparing base (ba85175) to head (1ded963).
Report is 6 commits behind head on main.

Files	Patch %	Lines
crates/polars-io/src/parquet/write/options.rs	50.00%	17 Missing ⚠️
...ates/polars-io/src/parquet/write/batched_writer.rs	91.76%	14 Missing ⚠️
crates/polars-io/src/parquet/read/options.rs	0.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15860      +/-   ##
==========================================
+ Coverage   80.39%   81.37%   +0.98%     
==========================================
  Files        1263     1382     +119     
  Lines      165368   176827   +11459     
  Branches        0     3032    +3032     
==========================================
+ Hits       132941   143890   +10949     
- Misses      32427    32449      +22     
- Partials        0      488     +488     

Flag	Coverage Δ
python	74.76% <89.35%> (?)
rust	78.50% <89.35%> (?)

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