feat: Add required: bool to ParquetFieldOverwrites

[coastalwhite]

Fixes #17418.

This adds the required: bool field to ParquetFieldOverwrites which allows exported fields to be marked as Parquet required. This will also mark the Arrow field as not nullable.

This works for all nesting levels.

import polars as pl
from polars.io.parquet import ParquetFieldOverwrites

f = io.BytesIO()
pl.Series("a", [[1], [2, 3], [3, 4, 5], None]).to_frame().lazy().sink_parquet(
    f,
    field_overwrites=ParquetFieldOverwrites(
	name="a",
	required=False,
	children=ParquetFieldOverwrites(required=True),
    ),
)

import pyarrow.parquet as pq

f.seek(0)
schema = pq.read_schema(f)
assert schema.field(0).nullable
assert not schema.field(0).type.value_field.nullable

[codecov]

Codecov Report

Attention: Patch coverage is 94.28571% with 2 lines in your changes missing coverage. Please review.

Project coverage is 80.36%. Comparing base (ba1293c) to head (e701b90).
Report is 2 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-parquet/src/arrow/write/mod.rs	75.00%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #23013      +/-   ##
==========================================
- Coverage   80.38%   80.36%   -0.03%     
==========================================
  Files        1682     1682              
  Lines      223374   223403      +29     
  Branches     2803     2804       +1     
==========================================
- Hits       179562   179529      -33     
- Misses      43145    43212      +67     
+ Partials      667      662       -5     

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