RTM waveforms stop on whatever value they're on when asked to stop playing waveform

[swh76]

Describe the bug

Need a work around for this, otherwise when users play waveforms and then stop them they will likely be left on an indeterminate bias. More details on the issue are logged on this JIRA ticket:
https://jira.slac.stanford.edu/browse/ESCRYODET-394

[swh76]

@jmdewart I implemented this to stop TES waveforms:

pysmurf/python/pysmurf/client/util/smurf_util.py

Line 4149 in fabc41f

def stop_tes_bipolar_waveform(self, bias_group, **kwargs):

is there a better way to do this such that it always stops with the value the DACs were set to before the TES waveform started playing? Or better to implement in pysmurf by caching the DAC settings or something whenever a waveform starts playing?