Watch the picture form one sampling step at a time and stop a run that is
going wrong. Step Preview needs no wires and shows whichever sampler is
working, with Stop and Stop all. Save Image and Save Video get a steps
switch, off by default, that shows the steps where the saved picture goes,
with a Stop button.
A queued workflow that shows its steps asks ComfyUI for the auto preview
method for that run, only when no method was chosen in the frontend or on
the command line.