Use nextest config for fine-tuning tests

we ran into an issue resolved by this commit: https://github.com/stacks-network/stacks-core/pull/5296/commits/82c36d7e544b384f5a7942a12b8a750660622206

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.

https://nexte.st/docs/configuration/per-test-overrides/ https://nexte.st/docs/configuration/test-groups/