Describe the desired feature

Currently, it seems like Echidna uses a single core/process/thread to shrink failed sequences.

In some cases, however, we're interested in using 100% of the machine's resources to extract the results of that particular sequence. For example, this is often the case when I am using stopOnFail: true and workers: N in a multicore setup. I don't care about other failed properties, I only care about that particular one that I know to have failed. The problem is that this takes forever even if I bump up N or the number of cores.

It seems like trying to shrink a sequence on a c5.large instance takes about the same amount of time as on a c5.4xlarge (benchmark pending), which is unexpected.