Convert the OAV to ophyd-async

[DominicOram]

We should try and get all our devices into ophyd-async. The OAV is one of the last ones left

Note

This is a reasonably large device, it may make sense to split it into multiple issues

Acceptance Criteria

• The OAV is converted into ophyd-async
• Tests all still pass

[DominicOram]

#801 should be done first

[DominicOram]

As part of this we should probably look at how we do the OAVConfigParams. Particularly how they get updated from the device. It may make more sense for them to be derived signals bluesky/ophyd-async#525

[noemifrisina]

As this is a fairly large device and we probably can't have an ophyd-async device with ophyd components (or viceversa), the first step will be to make a new very basic ophyd-async device meeting the minimum needs for i24 serial and then we can add the rest of the functionality as we go along.