fix(python): support Polars datetime literals and timezone expressions

[danking]

Polars datetime literals can serialize as Scalar.Datetime or a literal wrapped in ReplaceTimeZone, causing Vortex predicate conversion to fail. Decode datetime scalars and map timezone replacement to the native Vortex function provided by the base PR, without evaluating expressions in Polars during conversion.

Share datetime decoding across serialization variants, unwrap timezone metadata, and set nullability from whether the value is null. Add file-scan and expression regressions for timestamp units, timezone removal, DST policies, policy columns, and serialization.

This PR is stacked on #10182, which adds native replace_time_zone.

Validation: 1 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 1 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. The full datetime/timezone selection also passed all 41 cases; comparison literals explicitly match the tested timestamp unit. No lint or broader suite was run.

[codspeed]

Merging this PR will improve performance by 10.09%

⚠️ 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 benchmark measured no execution time

Nothing ran under measurement, usually because the compiler removed the code under test. This result is not comparable, so it counts as unchanged.

Preventing compiler optimizations

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 1 improved benchmark
✅ 2182 untouched benchmarks
⏩ 409 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	WallTime	words_gather_dispatch_neon[65536]	2.3 µs	2.1 µs	+10.09%
⚠️	Simulation	bench_compare_primitive[(10000, 2)]	64.6 µs	< 1 ns	N/A

Tip

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_{Comparing dk/polars-datetime-literals (e5859a0) with develop (1ee4e3a)}

Footnotes

1. 409 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. ↩