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
9 files changed