Goal: Introduce a dedicated tox environment that starts an oslo.service-backed app with active threads, then forks via multiprocessing to validate absence of deadlocks on Linux and macOS runners.

Acceptance Criteria:

• Verify new tox job py3X-spawn-safety executes in CI.

• Test fails if any call blocks > 10 seconds.

• CI job runs on every PR and in gate pipeline.

Additional Details:
See https://pythonspeed.com/articles/python-multiprocessing/ and video explanation at https://youtu.be/RIc-Tut95YM?t=185.