[xixihaha-ha]

Line3.intersect_plane() can return None for perpendicular lines and planes after rescaling their homogeneous representations. For example:

line = Line3.PointDir([1, 2, 3], [0, 0, 1e-8])
plane = Plane3([0, 0, 1e-8, -5e-8])
line.intersect_plane(plane)  # None; intersection should be [1, 2, 5]

Scale the parallelism threshold by both direction and normal norms, so tol tests angular separation independently of their magnitudes. The intersection formula and return structure are unchanged.

Regressions cover signed rescaling, near-parallel tolerance, point/parameter consistency, and parallel lines. Five new subcases fail on unchanged 25b19b3; all eleven pass with the fix. Full suite on Windows/Python 3.11.14: 568 passed, 4 skipped, 110 subtests passed. Black 23.10.0 and git diff --check pass.

Prepared and validated with OpenAI Codex assistance.