[NB] Add `sweep_channels_slow` method...
[NB] Add `sweep_channels_slow` method...

Add `sweep_channels_slow` method which uses one firmware call per
channel, as opposed to scanning all channels with a single firmware call
as in `sweep_channels` method.

wheeler-microfluidics/dmf-control-board-firmware,wheeler-microfluidics/dmf-control-board-firmware,wheeler-microfluidics/dmf-control-board-firmware,wheeler-microfluidics/dmf-control-board-firmware