tests: refactor test setups towards fixtures and hinting (#968) * refactor test setups towards fixtures and hinting * cleanup * emitter: EventEmitter * fixup protocol * if TYPE_CHECKING: for the TestEventQueue type alias * give in * isort * apply to other tests * fixup * rename tests.util to tests.utils * isort * flake8 * stop using a (nonexistant) emitter fixture * formatting