Use nextest config for fine-tuning tests

what was happening was that the test in the commit above was timing out on a remote runner, but passing locally. likely due to this issue in their docs: https://nexte.st/docs/configuration/threads-required/?h=threads

for the above test, i was able to confirm that using that threads-required flag for this specific test allowed it to pass.

i think we should be able to utilize this config to more finely-tune how we run tests locally and on remote blackboxes to reduce transient failures.

stacks-network / stacks-core