Fix concentric infill generating inside holes (dome/cavity cross-sections)

[Copilot]

• Understand the bug: concentric infill skipped entire loops based on 50% point-in-hole sampling, so loops that partially overlapped holes were printed entirely — including portions inside the hole
• Fix concentric.coffee: when holes exist, clip each loop edge by edge using clipLineWithHoles, group resulting valid segments into polylines, render each polyline with combing travel moves
• Add regression test using ExtrudeGeometry (rectangular outer boundary + circular inner hole) that specifically tests the partial-overlap scenario
• Address review comment #2868826589: extract parseFillExtrusionCoords helper to eliminate duplicated G-code coordinate parsing across both hole tests
• Address review comment #2868826571: hoist HOLE_TOLERANCE = 0.5 as a shared describe-scope constant; apply to both hole-radius assertions to absorb polygon-approximation boundary noise
• Address review comment #2868826580: replace for polyline in polylines with nearest-neighbour while loop (picks closest start/end, optionally flips polyline) to minimise travel in holes-present branch
• Simplify remainingPolylines.length > 1 guard to just if lastEndPoint? per secondary review feedback
• All 7 concentric infill tests pass

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[Copilot]

Pull request overview

Fixes concentric infill so it no longer generates extrusion paths inside holes (notably in dome/cavity-like cross-sections) by switching from point-sampling “skip loop” logic to geometric line clipping against hole boundaries.

Changes:

• Replace majority point-sampling hole detection with per-edge clipLineWithHoles clipping and polyline rendering when holes exist.
• Remove the unused primitives import and add clipping dependency in the concentric pattern.
• Add a regression test covering a rectangular loop intersecting a circular hole (the previously missed 50% sampled-points case).

Reviewed changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 4 comments.

File	Description
src/slicer/infill/patterns/concentric.coffee	Clips concentric loop edges against holes and renders the remaining segments as polylines to prevent infill inside holes.
src/slicer/infill/patterns/concentric.test.coffee	Adds a regression test for partial-overlap rectangular-vs-circular hole cases and keeps/extends hole-avoidance assertions.

[jgphilpott]

@copilot apply changes based on the comments in this thread