refactor(rust): Refactor Schema to use generic struct from new polars-schema crate

[nameexhaustion]

• Removed, as cannot be impl'd for foreign type:
  • FromIterator<impl Into<Field>>
    • This was used extensively across the codebase, to avoid having to rewrite everything, we use a small hack:
      • For polars_schema::Schema, add FromIterator<impl Into<(PlSmallStr, D)>>
      • For polars_core::Field, we impl Into<(PlSmallStr, D)>
  • From<&[Series]>
    • Only used in 1 place, manually replaced with iter().map(|s| (s.name().clone(), s.dtype().clone())
  • From<&ArrowSchema>
    • Replaced all .into()s with fn Schema::from_arrow_schema

[nameexhaustion]

Generic functions moved from impl Schema from polars-core

[codecov]

Codecov Report

Attention: Patch coverage is 84.25532% with 37 lines in your changes missing coverage. Please review.

Project coverage is 79.85%. Comparing base (04d0978) to head (a9c7dc6).
Report is 43 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-schema/src/schema.rs	87.30%	24 Missing ⚠️
crates/polars-io/src/ipc/ipc_reader_async.rs	0.00%	4 Missing ⚠️
crates/polars-plan/src/plans/conversion/scans.rs	55.55%	4 Missing ⚠️
crates/polars-core/src/schema.rs	88.23%	2 Missing ⚠️
crates/polars-io/src/avro/read.rs	0.00%	1 Missing ⚠️
crates/polars-io/src/ipc/ipc_stream.rs	0.00%	1 Missing ⚠️
crates/polars-sql/src/sql_expr.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #18539      +/-   ##
==========================================
- Coverage   79.87%   79.85%   -0.02%     
==========================================
  Files        1501     1502       +1     
  Lines      201823   201828       +5     
  Branches     2868     2868              
==========================================
- Hits       161200   161178      -22     
- Misses      40077    40104      +27     
  Partials      546      546              

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[codspeed-hq]

CodSpeed Performance Report

Merging #18539 will not alter performance

_{Comparing nameexhaustion:polars-schema (a9c7dc6) with main (04d0978)}

Summary

✅ 37 untouched benchmarks

[nameexhaustion]

Failing CI is unrelated (uv)

Run uv pip install -r py-polars/requirements-dev.txt -r docs/requirements.txt
Resolved 158 packages in 1.39s
error: Failed to prepare distributions
  Caused by: Failed to fetch wheel: llvmlite==0.36.0
  Caused by: Build backend failed to determine extra requires with `build_wheel()` with exit status: 1
--- stdout:

--- stderr:
Traceback (most recent call last):
  File "<string>", line 14, in <module>
  File "/home/runner/.cache/uv/builds-v0/.tmpLksiJD/lib/python3.[12](https://github.com/pola-rs/polars/actions/runs/10695782907/job/29649770387?pr=18539#step:5:13)/site-packages/setuptools/build_meta.py", line 332, in get_requires_for_build_wheel
    return self._get_build_requires(config_settings, requirements=[])
           ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/home/runner/.cache/uv/builds-v0/.tmpLksiJD/lib/python3.12/site-packages/setuptools/build_meta.py", line 302, in _get_build_requires
    self.run_setup()
  File "/home/runner/.cache/uv/builds-v0/.tmpLksiJD/lib/python3.12/site-packages/setuptools/build_meta.py", line 503, in run_setup
    super().run_setup(setup_script=setup_script)
  File "/home/runner/.cache/uv/builds-v0/.tmpLksiJD/lib/python3.12/site-packages/setuptools/build_meta.py", line 3[18](https://github.com/pola-rs/polars/actions/runs/10695782907/job/29649770387?pr=18539#step:5:19), in run_setup
    exec(code, locals())
  File "<string>", line 55, in <module>
  File "<string>", line 52, in _guard_py_ver
RuntimeError: Cannot install on Python version 3.12.5; only versions >=3.6,<3.10 are supported.