feat(vortex-spatial): add convex hull scalar function

[HarukiMoriarty]

Summary

• add a strict native MultiPoint to Polygon convex-hull scalar function
• delegate planar hull computation directly to geo::ConvexHull
• preserve CRS and outer nullability while materializing native 2-D Polygon storage
• use shared unary dispatch for constants and strict null propagation
• cover empty, one-point, collinear, nullable, constant, and Q5-style collect-to-hull-to-area execution
• add a dedicated convex-hull microbenchmark

Semantics

The return dtype is always native Polygon, including empty and degenerate hulls. Consistent with the current geometry-kernel policy, coordinate finiteness is unchecked unless validation is explicitly enabled; this function does not add per-call NaN validation.

[codspeed-hq]

Merging this PR will improve performance by 42.66%

⚡ 2 improved benchmarks
✅ 1947 untouched benchmarks
🆕 3 new benchmarks
⏩ 85 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Simulation	decompress[u64, (1000, 16)]	133.4 µs	72.7 µs	+83.44%
⚡	Simulation	compress_fsst[(1000, 64, 8)]	1.2 ms	1 ms	+10.95%
🆕	Simulation	eight_points	N/A	3.8 ms	N/A
🆕	Simulation	nullable_eight_points	N/A	3.8 ms	N/A
🆕	Simulation	sixty_four_points	N/A	15.4 ms	N/A

Tip

Curious why this is faster? Comment @codspeedbot explain why this is faster on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing nemo/geo-convex-hull (a49acef) with nemo/geo-collect (1f9f067)}

Footnotes

1. 85 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. ↩