Generalizes get_dummy_appointment (there were multiple instances of it in different tests)

Also refactors some unused imports and modifies the watcher tests to use .serialize instead of to_json

test/unit/test_appointment.py

@@ -10,7 +10,6 @@ from test.unit.conftest import get_random_value_hex
 c_logger.disabled = True
 
 # Not much to test here, adding it for completeness
-
 @fixture
 def appointment_data():
     locator = get_random_value_hex(32)