fix: Handle strictness for Decimal Series construction

[stinodego]

Ref #14427

Changes

• Implement casting for AnyValue to Decimal
• Update AnyValue constructors to properly apply the strict parameter. This means that the following will raise unless strict=False is set:
  • Mixing Decimals with non-decimals
  • Mixing Decimals with different scales
  • Decimals that do not match the given dtype

[codecov]

Codecov Report

Attention: Patch coverage is 86.44068% with 8 lines in your changes missing coverage. Please review.

Project coverage is 80.99%. Comparing base (7ebcfab) to head (bbe5fc7).
Report is 4 commits behind head on main.

Files	Patch %	Lines
crates/polars-core/src/series/any_value.rs	82.85%	6 Missing ⚠️
crates/polars-core/src/datatypes/any_value.rs	89.47%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #15309      +/-   ##
==========================================
+ Coverage   80.98%   80.99%   +0.01%     
==========================================
  Files        1445     1445              
  Lines      189925   189959      +34     
  Branches     2712     2713       +1     
==========================================
+ Hits       153808   153859      +51     
+ Misses      35618    35601      -17     
  Partials      499      499              

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[codspeed-hq]

CodSpeed Performance Report

Merging #15309 will degrade performances by 18.08%

_{Comparing av-strict-decimal (bbe5fc7) with main (7ebcfab)}

Summary

❌ 1 regressions
✅ 36 untouched benchmarks

⚠️ Please fix the performance issues or acknowledge them on CodSpeed.

Benchmarks breakdown

	Benchmark	main	av-strict-decimal	Change
❌	test_groupby_h2oai_q5	1.9 ms	2.3 ms	-18.08%