mx-bluesky unit tests taking ~3x longer since signal-typing changes

[rtuck99]

Since updating mx-bluesky to be compatible with #594, the unit tests are taking significantly longer to complete.
On my desktop machine the difference is ~97s to complete compared to ~27s before

It seems that most of this slowdown is due to waiting in call_in_bluesky_event_loop() waiting for wait_for_connection(coros=device.connect(mock=True)) to complete.

Can this be made faster?

[coretl]

Can you post a typical test please?

[olliesilvester]

See https://github.com/DiamondLightSource/mx-bluesky/blob/3845a51a2f083c578b92476702950f4125813b4b/tests/unit_tests/beamlines/i04/test_thawing.py#L118 for a typical test

In our tests, devices are created through fixtures which look like
smargon = i03.smargon(fake_with_ophyd_sim=True)

which in turn calls
call_in_bluesky_event_loop(...) and the ophyd-async wait_for_connection(..)

[DominicOram]

I'm happy this is fixed by #641