Vector implements IEquatable<Vector> with proper GetHashCode for HashSet usage.
Polygon.FindCrossing uses bounding-box pruning to skip non-overlapping edge pairs.
Helper.DirectionalDistance deduplicates vertices via HashSet, sorts edges for
early-exit pruning, and adds a new array-based overload that avoids allocations.
PartBoundary sorts directional edges and exposes GetEdges for zero-alloc access.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
