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>