Reconsideration of the OP_RUN request message operation

[nsoblath]

Previously there was a 4th request message operation, OP_RUN, and I'd like to consider the possibility for putting it back in. OP_RUN was removed from the standard a while ago, but never completely removed from the codebase. You cannot currently send an OP_RUN, but some of the code for handling such messages still exists.

Psyllid has a use case where sending a "run" command would make sense. In fact, the Psyllid API still has the ability to receive OP_RUNs, plugging into the parts of dl-cpp that still exist for handling them. Psyllid has a distinct "running" state, when it's taking data.

From discussion on the Project 8 Slow Controls call (5/2/24), other opportunities for using this type of request would be mass spectrometers, and (based on the Phase II experiment) the RSA.