Make an ADR on signal types and enforce

[DominicOram]

Following #310 (comment) we have a well defined list of types that signals are allowed. However, there are still old devices in dodal that use different types e.g. https://github.com/DiamondLightSource/dodal/blob/f2e63c2c55d49ed35cef73531be7d4bcceb42546/src/dodal/devices/zocalo/zocalo_results.py#L133. To make sure these get phased out and more don't get introduced we should prohibit other types ideally through the typing system. To make it clear why this is the case we should make an ADR too.

Acceptance Criteria

• An ADR is made on the types that signals are allowed
• If try and make a signal with an unsupported type e.g. soft_signal_r_and_setter(MyArbitraryType) the type system will complain

[coretl]

Agreed.

#594 will do the type checking.

https://github.com/bluesky/ophyd-async/pull/594/files#r1790651259 shows the types that will be in the ADR