feat: geometric diversity for synthetic assembly generation
- Add AxisStrategy type (cardinal, random, near_parallel)
- Add random body orientations via scipy.spatial.transform.Rotation
- Add parallel axis injection with configurable probability
- Add grounded parameter on all 7 generators (grounded/floating)
- Add axis sampling strategies: cardinal, random, near-parallel
- Update _create_joint with orientation-aware anchor offsets
- Add _resolve_axis helper for parallel axis propagation
- Update generate_training_batch with axis_strategy, parallel_axis_prob,
grounded_ratio parameters
- Add body_orientations and grounded fields to batch output
- Export AxisStrategy from datagen package
- Add 28 new tests (72 total generator tests, 158 total)
Closes #8
forbes-0023
78289494e2