Adds immutable VariableDefinition record to OpenNest.CNC with name,
expression, resolved value, inline, and global flags. Fixes namespace
collision in PatternTilerTests and PolygonHelperTests caused by the new
OpenNest.Tests.CNC namespace.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
Move 43 root-level test files into feature-specific subdirectories
mirroring the main codebase structure: Geometry, Fill, BestFit, CutOffs,
CuttingStrategy, Engine, IO. Update namespaces to match folder paths.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
