Add regression test for nested enter dispatch in queued state machine

[pgularski]

Summary

• Add a regression test for issue Not returning to initial state after exit #9 covering nested enter dispatch in a queued state machine
• Verify the machine returns to the initial state after the nested transition sequence completes
• Confirm the nested composite state resets its counter and leaf state as expected

Testing

• Added unit test coverage in test/test_queued.py
• Not run (not requested)