Python-redux

- fix: initial snapshot cleanup which used to mistakenly remove files with store:... filenames now removes files with store-... filenames

- chore: changed the format of snapshot filenames from store:... to store-...

- chore(test): move fixtures and testing utilities to `redux-pytest` package
- feat(test): add `wait_for`, `store_monitor`, `event_loop` and `needs_finish` fixtures
- test: add tests for scheduler and fixtures
- refactor: `SideEffectRunnerThread` now runs async side effects in its own event-loop
- refactor: removed `immediate_run` from event subscriptions
- refactor: removed `EventSubscriptionOptions` as the only option left was `keep_ref`, it's now a parameter of `subscribe_event`
- feat: new `on_finish` callback for the store, it runs when all worker threads are joined and resources are freed

- fix: automatically unsubscribe autoruns when the weakref is dead
- fix: use weakref of event handlers in `event_handlers_queue`

- refactor: drop logging fixture and use standard pytest logger in tests

- refactor: add cleanup to `FinishEvent` handler to clean workers, listeners, subscriptions, autoruns, etc
- refactor: `TaskCreator` add `TaskCreatorCallback` protocols
- refactor: `Store._create_task` now has a callback parameter to report the created task
- refactor: move serialization methods and side_effect_runner class to separate files