Fix/value readout
This MR fixes the readout of a specific value on this device, using the scpiml library.
The deal is that the hardware sends back not a single value, but a list, with two other pointless (for our usage) parameters.
The library assumes that the bytes read back from the hardware can be directly cast to the right datatype.
Here, as we get a list, we first need to get the first element (the actual value.)
To do so, I implemented a custom setter. But we also need a custom parser where, if we can't cast the value, we simply return it, and hope that the setter can handle it (spoilers: it does.)
I also implemented another couple of requests from the instrument scientists, where they desired drop-downs as opposed to free-fields.