mix mneme.watch: Immediately halt test suite on reload

[zachallaun]

Let's say you're running mix mneme.watch and you're being prompted on test 5 of 10. Instead of accepting the prompt, you make a change to some file and save.

Current behavior: The prompt is interrupted, the assertion is skipped, and the remaining tests run before restarting, skipping any assertions that would have failed. In this example, tests 6-10 still run.

Desired behavior: The prompt is interrupted and testing immediately stops. Tests 6-10 do not run.