feat(python): Support Decimal inputs for lit

[stinodego]

Closes #13341

Previously, passing Python Decimal objects to lit was unsupported. Now it works:

from decimal import Decimal
import polars as pl

expr = pl.lit(Decimal("0.1"))
print(pl.select(expr))

shape: (1, 1)
┌──────────────┐
│ literal      │
│ ---          │
│ decimal[*,1] │
╞══════════════╡
│ 0.1          │
└──────────────┘

[alexander-beedie]

Closes #13341 👍

[stinodego]

Parsing logic for lit should be unified with that of AnyValue. For now, this works...

[codspeed-hq]

CodSpeed Performance Report

Merging #16950 will improve performances by 27.51%

_{Comparing lit-decimal (ce6838d) with main (d8e4a61)}

Summary

⚡ 1 improvements
✅ 36 untouched benchmarks

Benchmarks breakdown

	Benchmark	main	lit-decimal	Change
⚡	test_groupby_h2oai_q7	2.6 ms	2 ms	+27.51%

[codecov]

Codecov Report

Attention: Patch coverage is 80.00000% with 2 lines in your changes missing coverage. Please review.

Project coverage is 80.98%. Comparing base (d8e4a61) to head (ce6838d).

Files	Patch %	Lines
crates/polars-plan/src/logical_plan/lit.rs	66.66%	1 Missing ⚠️
py-polars/src/lazyframe/visitor/expr_nodes.rs	0.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   #16950      +/-   ##
==========================================
+ Coverage   80.96%   80.98%   +0.01%     
==========================================
  Files        1445     1445              
  Lines      189916   189925       +9     
  Branches     2712     2712              
==========================================
+ Hits       153771   153803      +32     
+ Misses      35645    35623      -22     
+ Partials      500      499       -1     

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