gh-128041: Add terminate_workers and kill_workers methods to ProcessPoolExecutor

[csm10495]

Provides a way to forcefully stop all the workers in the pool

Typically this would be used as a last effort to stop all workers if unable to shutdown / join in the expected way.

This is a newer version of #128043 that includes fixes for transient issues seen in CI.

• Issue: Add terminate_workers to ProcessPoolExecutor #128041

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📚 Documentation preview 📚: https://cpython-previews--130849.org.readthedocs.build/

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @gpshead for commit ec7599c 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F130849%2Fmerge

If you want to schedule another build, you need to add the 🔨 test-with-buildbots label again.

[csm10495]

I've run

./python.exe -m test test.test_concurrent_futures.test_process_pool  -vvv --fail-env-changed

75 times in a row now without a failure. @colesbury mind checking again. Thanks for the feedback!

[bedevere-bot]

🤖 New build scheduled with the buildbot fleet by @colesbury for commit 92a2d72 🤖

Results will be shown at:

https://buildbot.python.org/all/#/grid?branch=refs%2Fpull%2F130849%2Fmerge

If you want to schedule another build, you need to add the 🔨 test-with-buildbots label again.

[colesbury]

Thanks @csm10495, this looks good to me!

I rescheduled the buildbots and I'm also running some stress tests locally. So far, it looks good!

[csm10495]

I don't think those buildbot failures are related, but not 100% sure.