Wraps FillExtents in an IFillStrategy, trying both bestRotation and
bestRotation+90° angles and picking the better result. Reads
BestFits from SharedState (populated by PairsFillStrategy) to allow
FillExtents to search the best-fit cache for improved pair geometry.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>