test_runner: fix run() isolation=none hang in cluster workers

[inoway46]

Summary

• fix a hang in run() when using isolation=none in cluster workers
• trigger teardown for run() API consumers without waiting on beforeExit
• limit the explicit teardown path to run() API usage (!isTestRunner) to avoid changing node --test semantics
• add a regression test for the cluster worker scenario

Test

• ./tools/test.py test/parallel/test-runner-run.mjs
• ./tools/test.py test/parallel/test-runner-extraneous-async-activity.js
• ./tools/test.py test/parallel/test-runner-no-isolation.mjs test/parallel/test-runner-no-isolation-hooks.mjs

[nodejs-github-bot]

Review requested:

• @nodejs/test_runner