gimlet-seq-server: use set_bytes not write_bytes for sequencing control

[Aaron-Hartwig]

Fixes #1929

Since write_bytes uses the Write operation, we effectively clear the A1 bit when setting the A0 bit. Using set_bytes uses a BitSet operation, allowing us to set A0 while leaving A1 in place. The FPGA has papered over this by ignoring the A1 bit while it is in A0.

[nathanaelhuffman]

I concur. Without this, we're actually commanding the A1 state machine back to IDLE, but it holds the A1 rails up because A0 rails are still up and we have sequencing requirements so everything "works" even though this was currently wrong.