fix: ping fails when a process is blocking GIL

[deanq]

Solution: run ping heartbeat in a separate Python process to its own GIL.

Tested by overriding an Endpoint's Docker Configuration > Container Start Command with:

/bin/bash -c "apt-get update && \
apt-get install -y git && \
pip install git+https://github.com/runpod/runpod-python@fix-unblock-ping --no-cache-dir && \
<insert original START CMD>"

[justinwlin]

LGTM! Thanks for the fix on timeout issues.