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>
AJ Isaacs
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