Synchrotron: Add linking device logic

[abbiemery]

As stated in the README, the Synchrotron device is just a collection of unconnected simualted iocs. The topup, currrent, countdowns etc all have behavior that can be simulated and linked with the inputs & output busses.

[abbiemery]

As stated in issue #3 , the goal was a minimum working device. It would be ideal to now have the device behave slighlty more naturally and implement the topup gating behaviour of the records

Required:

• Include internal logic to link the top-up timers and the current (See high level apps confluence for Top UP gating).

[DominicOram]

For testing Artemis it would be useful to have a backdoor for this (DiamondLightSource/tickit#83 is the best way to do this but in the meantime we can just have a PV that we can write to from ophyd)

[abbiemery]

That is the easiest way for now, having a writable PV is a one line addition in the epics adapter.

(See the femto device in the tickit repo for PV's that are caput able.)

[abbiemery]

Something else that would be nice for this ticket : Changing the PV names to all be prefixed with S03-SIM (or something similar) instead of BL03S, since BL03S is a beamline prefix and the synchrotron is beamline agnostic.

[JimboMonkey]

I think the machine PVs within 'synchrotron' should stay as close to the 'real' PVs as possible, but with some kind of designation of simulation in there. eg SR-CS-FILL-01:ENDCOUNTDN could become SR-SIM-FILL-01:ENDCOUNTDN, and CS-CS-MSTAT-01:MODE could become CS-SIM-MSTAT-01:MODE

[abbiemery]

@evalott100 is this finished? Please may you check over it and close it if so.