The 0.022 margin assumed validators flatten arcs at 0.01; NestValidator
uses 0.001, so a pair can read at most 0.002 closer than true. 0.003
covers that plus the 1e-4 Clipper grid, returning ~0.019 per gap. Arc,
disc, obround and zero-spacing tests still pass.
Part geometry filtered only rapids, so scribe/etch moves counted as
material - the bug OpenNest fixed in 1b5e1b1. Use SpecialLayers.IsMaterial.
Co-Authored-By: Claude Opus 5.5 <noreply@anthropic.com>