Allow Plans to Handle FailedPause

[callumforrester]

The RunEngine can be paused mid-execution of a plan. It will ask the ophyd(-async) devices it is currently using to .pause() if they are Pausable. They may throw a FailedPause exception if anything goes wrong. The RunEngine does not currently handle this behaviour very well, it just stops abruptly and raises an exception.

Desired Behaviour

When a device fails to pause, the RunEngine should effectively cancel the pause and keep going. The user should be altered to what happened via a warning or sensible exception.

Possible Solution

@tacaswell started a WIP PR to handle this: #1634, so acceptance criteria for this issue is that PR is finished off and merged. See PR discussion for remaining work to be done.