korad-kaxxxxp: add quirk for long processing times of commands

korad-kaxxxxp: add quirk for long processing times of commands

Some Korad compatibles are said to take rather long a time between
reception of adjacent commands. It's not just that the response is
delayed, or that execution takes a long time. It's worse in that the
next request isn't received, and later responses don't correspond
to the requests which host software associates them with. A driver
implementation detail then "reads" 0.000 current values when the
PSU failed to respond to the "IOUT?" request.

Add a quirk flag. Allow for extra processing time after SET commands
and the GET command for STATUS. Add the Velleman PS3005D V1.3 model
with this quirk. Behaviour does not change for other devices.

This implementation is based on a submission that was provided by
Pilatomic <redacted>.