RotationDirection and direction filtering were recomputed on every
GetLines call. Pre-compute edges per PushDirection once in the
constructor so GetLines only translates cached edges.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
Extract offset polygon computation into PartBoundary, which builds
and caches inflated boundary polygons per unique part geometry.
FillLinear now uses symmetric half-spacing and reuses boundaries
across tiling passes, avoiding redundant offset calculations.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
