Lakeshore218: Show disabled sensors as disabled

As an instrument scientist, I want to specify which Lakeshore 218 sensors are disabled and not see any readings from them so that I don't get confusing readings which are over 400K from the Lakeshore 218 from sensors which are not connected.

Currently, the Lakeshore 218 reads values from disabled channels. These channels then show high temperatures as the PV values even though it says disabled on the front of the Lakeshore 218 box. These high-temperature readings are confusing for instrument scientists/users.

This ticket arose from helping TOSCA instrument scientists after migrating TOSCA to IBEX.

### Acceptance Criterion

- [ ] I can disable a sensor on the IOC level and not get a reading from the Lakeshore 218.
- [ ] The block value of a disabled sensor is sensible (e.g. 0)
- [ ] The PVs associated with a channel which is disabled do not go into an alarmed state.