Replace recursive FillRecursive with flat FillGrid that tiles along primary
axis, then perpendicular. Extract FindPlacedEdge, BuildRemainingStrip,
BuildRotationSet, FindBestFill helpers. Use array-based DirectionalDistance
to eliminate allocations in FindCopyDistance and FindPatternCopyDistance.
Simplify FindSinglePartPatternCopyDistance to delegate to FindCopyDistance.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>