feat(vortex-geo): add MultiPolygon extension type + WKB export for native geometry

[HarukiMoriarty]

Summary

Adds a native MultiPolygon geometry extension type to vortex-geo, and a WKB-export helper (to_wkb) for the native geometry types (Point, Polygon, MultiPolygon).

MultiPolygon (vortex.geo.multipolygon) mirrors the existing Polygon type, mainly for SpatialBench z_boundary column, which is mixture of Polygon and MultiPolygon.

to_wkb serializes a native geometry array to WKB (via geoarrow-cast), the form DuckDB's GEOMETRY vectors carry, for communicate with DuckDB.

What APIs are changed? Are there any user-facing changes?

Purely additive, new public API in vortex-geo:

• extension::MultiPolygon, the new extension type (with its ExtVTable + Arrow import/export).
• extension::{PointData, PolygonData} + to_wkb on the existing Point/Polygon types.

[codspeed-hq]

Merging this PR will not alter performance

⚠️ 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.

⚡ 2 improved benchmarks
❌ 1 regressed benchmark
✅ 1586 untouched benchmarks
⏩ 4 skipped benchmarks¹

Warning

Please fix the performance issues or acknowledge them on CodSpeed.

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
❌	Simulation	chunked_bool_canonical_into[(1000, 10)]	16.7 µs	26.8 µs	-37.55%
⚡	Simulation	bitwise_not_vortex_buffer_mut[128]	244.4 ns	215.3 ns	+13.55%
⚡	Simulation	bitwise_not_vortex_buffer_mut[1024]	304.7 ns	275.6 ns	+10.58%

Tip

Investigate this regression by commenting @codspeedbot fix this regression on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing nemo/geo-multipolygin (a3c046b) with nemo/spatial-wire-vx-bench (fdb0872)}

Footnotes

1. 4 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. ↩