Create DeviceMock for electron analysers drivers

[oliwenmandiamond]

Now that bluesky/ophyd-async#1129 has been merged, we should create DeviceMock for the electron analysers so testing is easier.

We need to set sensible default values, and when a region is set the array sizes are what we would expect to see and it returns "data" for spectrum and image.

Acceptance Criteria

• Default DeviceMock created for VGScientaAnalyserDriverIO and SpecsAnalyserDriverIO