[dev.fuzz] internal/fuzz: fail minimization on non-reproducible crash
workerServer.minimize now returns a response with Success = false when
the fuzz function run with the original input does not produce an
error. This may indicate flakiness.
The coordinator still records a crash, but it will use the unminimized
input with its original error message.
When minimization of interesting inputs is supported, Success = false
indicates that new coverage couldn't be reproduced, and the input will
be discarded.