Fix pixel drops at start of ramps

Ramps sporadically fail, where the actor cannot get enough pixels from the DAQ to complete the ramp. There is no per-read framing, so this is only discovered at the end of the ramp, and the drops could have come anytime.

On n1 at Subaru, we are seeing quite a few of these: 19/516 from 2023-05 to now, ~4%. It turns out that most/all ramps are simply missing pixels at the beginning of the ramp, visible even in the RESET frame. This is probably good news: even if we cannot fully recover that frame, it is essentially never used.

I have not yet found anything stupid on my side, sadly, nor seen warnings of SAM FIFO overflows. There are various counters on the SAM and the ASIC which can be reported more enthusiastically; I'll work on adding those under this ticket.