refactor(rust): Reduce size of ArrowDataType by boxing heavy variants

[orlp]

This reduces the size of ArrowDataType from 64 to 32 bytes.

[codecov]

Codecov Report

Attention: Patch coverage is 39.68254% with 76 lines in your changes missing coverage. Please review.

Project coverage is 78.95%. Comparing base (04004b8) to head (df9f62a).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
crates/polars-arrow/src/ffi/schema.rs	67.56%	12 Missing ⚠️
crates/polars-arrow/src/io/ipc/write/schema.rs	38.88%	11 Missing ⚠️
crates/polars-arrow/src/io/ipc/read/schema.rs	0.00%	9 Missing ⚠️
crates/polars-arrow/src/io/ipc/write/mod.rs	11.11%	8 Missing ⚠️
crates/polars-arrow/src/io/ipc/read/common.rs	14.28%	6 Missing ⚠️
crates/polars-parquet/src/arrow/write/schema.rs	0.00%	6 Missing ⚠️
crates/polars-arrow/src/datatypes/mod.rs	37.50%	5 Missing ⚠️
crates/polars-arrow/src/io/avro/read/schema.rs	0.00%	5 Missing ⚠️
crates/polars-row/src/encode.rs	0.00%	4 Missing ⚠️
crates/polars-core/src/series/from.rs	0.00%	3 Missing ⚠️
... and 4 more

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #20588      +/-   ##
==========================================
- Coverage   78.97%   78.95%   -0.02%     
==========================================
  Files        1564     1564              
  Lines      220807   220863      +56     
  Branches     2510     2510              
==========================================
+ Hits       174377   174389      +12     
- Misses      45855    45899      +44     
  Partials      575      575              

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