Improve cover state restoration from the HA entity cache (#412)

* Refresh cover state after the default timeout after restoring from the HA cache

This adds a timeout for movement states restored from the entity cache.

Uses #410 as a base.

* Implement checks to ensure a movement state is not restored if the device has already reached the movement extrema

- Updates tests to use a common mock cover device creation function to reduce code repetition

* Remove `_is_completely_open` property and init `_state` with None

- We init `_state` with None and let the `_determine_cover_state` function populate the value from current positions
- Ensures all lines are coverable by tests

* Ensure cover state restore and transition timer handles are cancelled upon entity removal

* Add tests for on_remove timer cancellations

* Make use of clear_transition methods to cancel timers on removal

* Test cleanup

* Add annotations for async_update test

* Consolidate cover calls to `maybe_emit_state_changed_event` into `_determine_cover_position` function

* Ensure position attributes are still updated when the state doesn't change

Author: jeverley