fix: add collinearity check to pointOnSegment() for diagonal wires

[valentinozegna]

Summary

• Add cross-product collinearity check to pointOnSegment() before the bounding-box test, preventing false net merges when diagonal wire bounding boxes overlap
• Use perpendicular distance tolerance of 2 units (0.0002 mil) to accommodate Altium coordinate rounding
• Clean up undefined keys (mpn, description) from Altium component output

Test plan

• New unit test for crossing diagonal wires with overlapping bounding boxes
• All 404 tests pass including golden file tests (no regressions)
• Type-check and lint clean

Closes #54