Use save/load for the Zebra

As a developer, it is difficult to work out the state of a Zebra since the majority of its PVs are changed outside of our `Bluesky` code, or never changed at all. This makes it complicated to make changes to, and means there's no easy way to return the Zebra to a 'safe state' if the settings are ever incorrect.

I propose that we identify which settings we ALWAYS want the Zebra to have, and then use ophyd-async's save/load during setup and cleanup to make sure it always starts and finishes in that state.