When a target count is known, ShrinkFiller now uses FillBestFit (fast
rectangle packing) to estimate how many parts fit on the full area,
then scales the shrink axis proportionally to avoid an expensive
full-area fill. Falls back to full box if estimate is too aggressive.
Also shrinks to targetCount (not full count) to produce tighter boxes
when fewer parts are needed than the area can hold.
IterativeShrinkFiller passes NestItem.Quantity as the target count.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Introduces IterativeShrinkFiller.Fill, which composes RemnantFiller and
ShrinkFiller by wrapping the caller's fill function in a closure that tries
both ShrinkAxis.Height and ShrinkAxis.Width and picks the better FillScore.
Adds IterativeShrinkResult (Parts + Leftovers). Covers null/empty inputs and
single-item placement with three passing xUnit tests.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
