Writable mathutils properties (Vector, Euler, etc.) were typed as plain
attributes with a union type, causing the getter to also return the union.
This made `obj.location.x` fail type checking since Sequence[float] has
no `.x`. Now these properties use @property for the getter (returning the
concrete mathutils type) and @setter accepting the wider union.
Co-Authored-By: Claude Opus 4.6 (1M context) <noreply@anthropic.com>