style: apply "black" formatting

meta.py

src/base/config.py

src/base/exceptions.py

src/base/logger.py

src/base/utils.py

src/client/client.py

src/client/connector.py

src/client/playerclient.py

src/engine.py

src/mixer.py

src/plugins/mailer.py

src/scheduling/api.py

src/scheduling/models.py

src/scheduling/programme.py

src/scheduling/scheduler.py

src/scheduling/utils.py

tests/test_config.py

tests/test_engine_executor.py

tests/test_logger.py