Add DegenerateToroidalSurface support and CDT edge preprocessing

[lucia3e8]

Summary

• Add DegenerateToroidalSurface as a torus variant in get_surface() — this STEP entity was unhandled, causing UnknownSurfaceType errors on component 693072010801
• Add CDT edge preprocessing in resolve_crossing_edges():
  • Point deduplication (dedup_close_points): snap nearly-coincident 2D boundary points to prevent phantom crossings from surface lowering numerical noise
  • T-intersection detection (point_near_segment): split constrained edges when a boundary vertex lies within ε of a non-adjacent edge, preventing CrossingFixedEdge from CDT exact predicates
  • Crossing resolution: when two constrained edges genuinely cross in 2D, split both at the intersection point by inserting a shared vertex

These fixes address CrossingFixedEdge errors on 4 components (XT30PW-F, SRP5030CA-4R7M, SRP6050CA-4R3M, KEY-SMD_4P) and the UnknownSurfaceType error on 693072010801.

Batch test improvement: 85/92 → 90/92 (92.4% → 97.8%)

Component	Issue	Fix
693072010801	DegenerateToroidalSurface not handled	Added as torus variant
XT30PW-F	CrossingFixedEdge on torus faces	CDT edge preprocessing
SRP5030CA-4R7M	CrossingFixedEdge	CDT edge preprocessing
SRP6050CA-4R3M	CrossingFixedEdge	CDT edge preprocessing
KEY-SMD_4P	CrossingFixedEdge (bowtie topology)	CDT edge preprocessing

Test plan

• cargo test passes
• Batch test against Diode component dataset: 90/92 pass (vs 85/92 baseline)
• No regressions on previously-passing components
• Verify 693072010801.step produces valid STL output
• Verify XT30PW-F.step no longer panics/errors

🤖 Generated with Claude Code

Stack: 1/4 — next: fix/degenerate-cylinder-lowering

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Note

Medium Risk
Medium risk: changes affect geometric preprocessing and constrained triangulation inputs, which can alter tessellation output and performance or introduce edge-case failures on complex faces.

Overview
Adds support for STEP DegenerateToroidalSurface by treating it as a torus in get_surface(), avoiding UnknownSurfaceType errors.

Hardens CDT input generation in resolve_crossing_edges() by deduplicating nearly-coincident boundary points, tightening/adjusting intersection tolerances, and adding a second pass to split edges on near vertex-on-edge (T) intersections, in addition to existing edge-edge crossing splits.

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Dedup can collapse into duplicate constraints

High Severity

After remapping close points, edges only removes self-loops. Distinct edges can collapse to the same undirected pair (including reversed order), leaving duplicate constrained edges that change CDT boundary parity and can misclassify interior/exterior regions.