Expose no-reset idle mode, and perhaps provide spare-read ramps.

By default, the ASIC continuously takes reset frames while idle, and continuously reads out during ramps.

We would like to take ramps where the ASIC is idle between reads, and where that idle time is variable.

The trivial part is exposing the knob to stop taking reset frames while idle. That may be enough. But see whether there is a sane way to fake up ramps by stitching nreset=0, nread=2 ramps together with sleeps.