Further prescale the muon detector shower line to reduce bandwidth

FYI @lohenry @hartmanl @lugrazet @isanders

Despite a prescale of 0.1, this is still one of the highest-bandwidth lines in Turbo, and recent tests show it jumping to 200 MB/s when we go to nominal mu. This is therefore a preemptive reduction of the prescale from 0.1 to 0.01.