Foundation for the geometry simplifier that will replace consecutive line
segments with fitted arcs. Adds ArcCandidate data class, GeometrySimplifier
with stub Analyze/Apply methods, and FitCircle using the Kasa algebraic
least-squares method. Also adds InternalsVisibleTo for OpenNest.Tests on
OpenNest.Core.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
