Compute the axis-aligned bounding box of a single stitch, normalizing the two stitch
shapes (cell-anchored x / y versus segment from / to) into one position-and-extent
value. Cell-anchored stitches occupy the unit square at their lower-left corner; segment
stitches span their two endpoints. The switch is exhaustive over Stitch kinds, so a
new kind that is neither cell- nor segment-shaped fails to compile until it is handled here.
Compute the axis-aligned bounding box of a single stitch, normalizing the two stitch shapes (cell-anchored
x/yversus segmentfrom/to) into one position-and-extent value. Cell-anchored stitches occupy the unit square at their lower-left corner; segment stitches span their two endpoints. The switch is exhaustive over Stitch kinds, so a new kind that is neither cell- nor segment-shaped fails to compile until it is handled here.