feat(vortex-geo): add Hilbert scalar function

[HarukiMoriarty]

Summary

• add vortex.geo.hilbert for native geometry columns with constant Rect bounds
• reuse the existing GeoEnvelope kernel and unary constant/column dispatch
• return nullable u32 Hilbert keys for spatial clustering
• add point and multipolygon Divan benchmarks

[codspeed-hq]

Merging this PR will not alter performance

✅ 1921 untouched benchmarks
🆕 2 new benchmarks
⏩ 43 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
🆕	Simulation	multipolygons	N/A	1.4 ms	N/A
🆕	Simulation	points	N/A	201.9 µs	N/A

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_{Comparing nemo/geo-hilbert-bounds (c0d4338) with nemo/geo-intersection-native (f2b5e90)}

Footnotes

1. 43 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. ↩