Fix purge test

[LuKks]

Unrelated, lots of space-unary-ops errors by Standard (probably a sub dep)

[HDegroote]

Great find!

Edit: below comments are not so relevant to the main problem you solved in this PR, because it's still possible for the 2 cores to start with the same 2 hex characters

I do think the problem can be solved in a different way, by making all tests which need a tmp dir use a helper, and by ensuring that the helper cleans up fully before finishing. Then we don't have to work around unintended side effects in the next test That would entail using the helper here: https://github.com/holepunchto/hyperdrive/blob/97f9ab89d4bc14ea346d6c96ae968eca73ce701b/test.js#L79 https://github.com/holepunchto/hyperdrive/blob/97f9ab89d4bc14ea346d6c96ae968eca73ce701b/test.js#L132 https://github.com/holepunchto/hyperdrive/blob/97f9ab89d4bc14ea346d6c96ae968eca73ce701b/test.js#L1397

And updating the helper to explicitly await the teardown, like here:

function createTmpDir (t) {
  const tmpdir = path.join(os.tmpdir(), 'hyperdrive-test-')
  const dir = fs.mkdtempSync(tmpdir)
  t.teardown(async () => await fs.promises.rm(dir, { recursive: true }))
  return dir
}

We could even add a sanity check before the dir creation, to rm it if there was one from an earlier run (for example if it was aborted midway), genre fs.rmSync('tmpdir', { recursive: true, force: true })

What do you think?