Chore: add type hints

src/aura_engine/base/config.py

src/aura_engine/core/client.py

src/aura_engine/core/mixer.py

src/aura_engine/engine.py

src/aura_engine/events.py

src/aura_engine/plugins/clock.py

src/aura_engine/plugins/monitor.py

src/aura_engine/scheduling/api.py

src/aura_engine/scheduling/scheduler.py

src/aura_engine/scheduling/timetable.py

tests/test_scheduling_scheduler_core_mock.py