The parallel-normal constraints (ParallelConstraint, PlanarConstraint,
ConcentricConstraint, RevoluteConstraint, CylindricalConstraint,
SliderConstraint, ScrewConstraint) and point-on-line constraints
previously used only the x and y components of the cross product,
dropping the z component.
This created a singularity when both normal vectors lay in the XY
plane: a yaw rotation produced a cross product entirely along Z,
which was discarded, making the constraint blind to the rotation.
Fix: return all 3 cross-product components. The Jacobian has a
rank deficiency at the solution (3 residuals, rank 2), but the
Newton solver handles this correctly via its pseudoinverse.
Similarly, point_line_perp_components now returns all 3 components
of the displacement cross product to avoid singularity when the
line direction aligns with a coordinate axis.
8e521b4519