fixes to sweep_benchmark.py + ppb arg
sweep device: prevent -ve step count
SH usable bins in capture device
twisted_async: drop scpi+vrt connections on disconnect
first cut of SH sweep
added iqin and dd rfe modes
fix SH sweep width
sweep device: remove automatic decimation
sweep device: reduce default min_points to 32
remove sweep decimated tests
added speca dd/iqin rfe mode