[dev.fuzz] internal/fuzz: notify coordinator for minimization
When a worker process finds a crasher, it now sends that result
directly to the coordinator without attempting to minimize it
first. The coordinator stops sending new inputs and sends the
unminimized crasher back to a worker (any worker) for minimization.
This prevents wasted work during minimization and will help us
implement -keepfuzzing later on. We may also be able to minimize
interesting inputs with this approach later.
Since panics are recoverable errors (they don't terminate worker
processes), we no longer attempt to minimize non-recoverable errors.
This didn't work too well before: we lost too much state.