Move fill algorithms to OpenNest.Engine.Fill namespace:
FillLinear, FillExtents, PairFiller, ShrinkFiller, Compactor,
RemnantFiller, RemnantFinder, FillScore, Pattern, PatternTiler,
PartBoundary, RotationAnalysis, AngleCandidateBuilder, and
AccumulatingProgress.
Move strategy layer to OpenNest.Engine.Strategies namespace:
IFillStrategy, FillContext, FillStrategyRegistry, FillHelpers,
and all built-in strategy implementations.
Add using directives to all consuming files across Engine, UI,
MCP, and Tests projects.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
