fix(python): support unsigned Polars scalar literals

[danking]

Polars predicate pushdown can serialize unsigned comparison literals as typed scalar variants that the converter rejects. Decode recognized scalar variants through the existing literal type mapping, including UInt8, UInt16, UInt32, and UInt64.

Add file-scan regression cases for comparisons on all four unsigned widths. Split from the original combined PR; datetime changes are in #10183 (stacked on #10182), and is_not_null changes are in #10184.

Validation: 4 targeted regression case(s) passed with this PR’s converter. With only polars_.py restored to the base revision and the same tests retained, all 4 failed with Polars ComputeError wrapping the unsupported-expression ValueError or NotImplementedError. The tests compare complete dataframes from Polars alone and a Vortex-backed Polars scan, and check explicit row expectations. No lint or broader suite was run.

[codspeed]

Merging this PR will improve performance by 12.86%

⚠️ Unknown Walltime execution environment detected

Using the Walltime instrument on standard Hosted Runners will lead to inconsistent data.

For the most accurate results, we recommend using CodSpeed Macro Runners: bare-metal machines fine-tuned for performance measurement consistency.

⚡ 1 improved benchmark
✅ 2174 untouched benchmarks
⏩ 534 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	WallTime	bitpack_blocked_compress_avx2	7.6 µs	6.7 µs	+12.86%

Tip

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_{Comparing dk/polars-predicate-pushdown (092e50d) with develop (c93ffa3)²}

Footnotes

1. 534 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

2. No successful run was found on develop (293d4f7) during the generation of this report, so c93ffa3 was used instead as the comparison base. There might be some changes unrelated to this pull request in this report. ↩