Address review: simulate TPDO reception, increase coverage to 62%

- Remove TestBaseNode402NextState: replaced by state setter tests
  that exercise the public .state property via TPDO/RPDO simulation
- Remove TestBaseNode402HomingStatus: replaced by TestBaseNode402Homing
  that calls _homing_status() with TPDO-injected statusword
- Remove test_supported_bitmask_unique: standard-defined values
- Remove TestBaseNode402TPDOCallback: implicitly covered by all tests
  using _inject_tpdo()

New test classes using TPDO reception simulation:
- TestBaseNode402StateTransition: full state machine transitions with
  _FakeRpdoVar simulating drive controlword/statusword exchange
- TestBaseNode402Homing: homing status via node._homing_status()
- TestBaseNode402OpMode: operation mode reading via TPDO/SDO fallback
- Extended TestBaseNode402State: check_statusword and statusword
  SDO fallback paths

Author: bizfsc