refactor(spatial): make bounding-box statistics explicit - #10837

Summary

Make spatial bounding-box statistics an explicit writer choice. Initializing vortex-spatial still registers geometry types, GeometryAabb, and spatial pruning rules, but no longer adds AABB statistics to zone maps automatically. Writers select file bounds with include_nested_statistics().with_file_statistics(...) and zone bounds through ZonedLayoutOptions::aggregate_fns.

Also fix spatial pruning for table files: the existing rules only recognized geometry columns at the expression root, so predicates such as ST_Intersects(geom, constant) could not use footer bounds for a struct field. The shared matcher now accepts direct and nested field paths while retaining the column-versus-literal restriction.

Changes

• Remove the unused zone_stat_default hooks and registry discovery from vortex-array and the zoned writer. Built-in zone defaults remain unchanged.
• Reuse the existing aggregate APIs and file format; no new core extension hook is introduced.
• Cover explicit and default statistics, cross-batch and nested file bounds, file pruning without zone maps, both spatial operand orders, and zone pruning with opt-in bounds.
• Document writer configuration and pruning limits: only supported ST_Intersects and ordered ST_Distance filters use the spatial rules; registering another compute function does not automatically enable pruning for it.

Validation

• Reviewed the full patch, comments, callers, and statistics/pruning paths.
• git diff --cached --check passed.
• Based on develop at 2e1b05b84.
• Local builds, tests, formatting, and lint commands were not run, following the repository's opt-in verification policy. The new regression cases have not been executed locally.