The two stripe layouts differ only in how far odd stripes shift, so they are
now one StaggeredFill with StaggerMode.HalfPitch (was FillEndOdd: half-pitch
shift, odd stripes one disc fewer) and StaggerMode.SlackShift (was
FillEndEven: shift by the stripe's leftover, every stripe full). The unused
FillEngine base and its throwing Fill(item, maxCount) go away. Layouts and
orientation tie-breaks are unchanged.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>
