BEND layer lines were being imported as cut geometry alongside the
separate Bend object detection, causing duplicate dark lines in nests.
Skip BEND layer entities in DxfImporter since bend detection reads
directly from the raw CadDocument.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>
Move DxfImporter, DxfExporter, NestReader, NestWriter, ProgramReader,
and Extensions into a new OpenNest.IO class library. The WinForms project
now references OpenNest.IO instead of ACadSharp directly.
Co-Authored-By: Claude Opus 4.6 <noreply@anthropic.com>
