refactor: update steering playout model

schemas/openapi-steering.json

src/aura_steering_api/models/__init__.py

src/aura_steering_api/models/nested_timeslot.py

src/aura_steering_api/models/playout_entry.py

src/aura_steering_api/models/playout_entry_episode.py

src/aura_steering_api/models/playout_entry_schedule.py

src/aura_steering_api/models/playout_entry_show.py