Variable compactUnusedVerticesConst

compactUnusedVertices: Fix = ...

Auto-fix for GEOMETRY_UNUSED_VERTICES — compacts positionsCompressed / normalsCompressed / uvsCompressed to keep only vertex slots referenced by indices or edgeIndices, and remaps both index arrays through the old-to-new slot map.

The geometry's AABB stays put — positions are still quantised against it, and dropping unused outliers can only shrink the actual content, never grow it. Recomputing a tighter AABB would change quantisation and therefore every surviving position; this fix takes the conservative path of leaving AABB alone.

Idempotent: returns {fixed: false} when every existing vertex slot is already in use.