test: adapt and fix playout models

src/aura_engine/scheduling/domain.py

src/aura_steering_api/models/timeslot.py

tests/json/steering-api-v1-playout.json

tests/test_engine_resources.py

tests/test_scheduling_api_fetcher.py

tests/test_scheduling_api_steering.py

tests/test_scheduling_domain.py

tests/test_scheduling_scheduler_core_mock.py

tests/test_scheduling_timetable.py