Find a good way to keep beamline and simulator devices in step

[DominicOram]

As a developer/scientist I would like to make to make sure that the devices for the simulated beamline are kept the same as those for the real one, with as much ease as possible. Currently to add a new device to e.g. i03/s03 I need to add the following to i03.py:

BEAMLINE_PREFIX = "BL03I"

def device():
     return MyDevice(prefix=f"{BEAMLINE_PREFIX}-BLAH")

Then the following to s03.py:

BEAMLINE_PREFIX = "BL03S"

def device():
     return MyDevice(prefix=f"{BEAMLINE_PREFIX}-BLAH")

Which is an exact replica, except the BEAMLINE_PREFIX. Ideally I should just need to add to i03.py and s03.py will update itself.

[DominicOram]

Originally I had something like:

from dodal import i03
i03.BEAMLINE_PREFIX = "BL03S"
i03.INSERTION_PREFIX = "SR03S"

from dodal.i03 import *

in s03.py but this causes big issues if importing s03 and i03 together. Alternatives could be to change the structure of i03.py into a class?

[DominicOram]

We might also want a fake_i03 that has all the i03 devices but as ophyd fake devices

[DominicOram]

As discussed with @callumforrester we can just do this with an env variable. We can check BEAMLINE and use i03 if it is that, otherwise s03