PushSelected now calls Compactor.Push instead of duplicating the push
logic. Compactor.Push moves parts as a group (single min distance) to
preserve grid layouts. Compact tries both left-first and down-first
orderings, iterating up to 20 times until movement drops below
threshold, and keeps whichever ordering traveled further.
Also includes a cancellation check in FillWithProgress to avoid
accepting parts after the user stops a nest.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Previously each moving part only checked against the original stationary
set. Parts pushed earlier in the loop were invisible to later parts,
causing overlaps (utilization > 100%). Now each pushed part is added to
the obstacle set so subsequent parts collide correctly.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
