fix(rust,python): Schema inconsistent on Decimal arithmetic with integer

[BhargavKumarNath]

Fixes a schema inconsistency where operations between a Decimal and an integer would preserve the original decimal precision during lazy schema inference (e.g. Decimal(10, 2)), while the actual physical runtime correctly operates using maximum precision Decimal(38, 2) (DEC128_MAX_PREC).

This PR updates schema.rs to explicitly handle Decimal op integer across +, -, *, and /, ensuring get_arithmetic_field and get_truediv_field correctly return Decimal(DEC128_MAX_PREC, scale) to match the eager runtime schema.

Tests Added a parametric test suite in test_arithmetic.py that verifies collect_schema() matches collect().schema for Decimal interactions against all 9 integer types (Int8 through Int128, UInt8 through UInt64) and basic operators.

I used AI to design the test suites.
I confirm that I have reviewed all changes myself, and I believe they are relevant and correct.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 81.56%. Comparing base (4f632e0) to head (0dfcd05).
⚠️ Report is 12 commits behind head on main.

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #28819      +/-   ##
==========================================
+ Coverage   81.51%   81.56%   +0.04%     
==========================================
  Files        1888     1888              
  Lines      266924   267749     +825     
  Branches     3240     3240              
==========================================
+ Hits       217594   218399     +805     
- Misses      48502    48522      +20     
  Partials      828      828              

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[BhargavKumarNath]

Fix complete. All checks passed