test: add unit tests for datagen modules
- test_types.py: JointType enum values/count, dataclass defaults/isolation
- test_pebble_game.py: DOF accounting, rigidity, classification, edge results
- test_jacobian.py: Jacobian shape per joint type, rank, parallel axis degeneracy
- test_analysis.py: demo scenarios (revolute, fixed, triangle, parallel axes)
- test_generator.py: chain/rigid/overconstrained generation, training batch
Bug fixes found during testing:
- JointType enum: duplicate int values caused aliasing (SLIDER=REVOLUTE etc).
Changed to (ordinal, dof) tuple values with a .dof property.
- pebble_game.py: .value -> .dof for constraint count
- analysis.py: classify from effective DOF (not raw pebble game with virtual
ground body skew)
105 tests, all passing.
Closes #6
forbes-0023
dc742bfc82