At-a-glance values of a run

It is easy to check which mnemonics are present in a run. It would be great, for the single valued ones that don't change, to give one value representative of the run.

There is one function for a KeyData, as_single_value(), but it is slow because it need to read the entire data array and throws an error if the value changed during the run.

Instead, we could use the CONTROL values, which are stored as single value (I think at the beginning of the run) for each variable. This way is fast to check on all mnemonics (~300 ms per run), but can be imprecise if the value changed during the run. For things like KB benders, motor positions, GATT, ESLIT, and lots of others that don't change during a run, this would be fine.