Extract distance computation from RotationSlideStrategy into a pluggable
IDistanceComputer interface. CpuDistanceComputer adds leading-face vertex
culling (~50% fewer rays per direction) with early exit on overlap.
GpuDistanceComputer wraps ISlideComputer with Line-to-flat-array conversion.
SlideOffset struct uses direction vectors (DirX/DirY) instead of PushDirection.
SpatialQuery.RayEdgeDistance(dirX,dirY) made public for CPU path.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>