Fix Docker runtimes not stopping

[tofarr]

End-user friendly description of the problem this fixes or functionality that this introduces

• Include this change in the Release Notes. If checked, you must provide an end-user friendly description for your change below
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Give a summary of what the PR does, explaining any non-trivial design decisions

This PR fixes an issue where Docker runtime containers were not being properly stopped when the application shuts down. The changes include:

Changes

1. Enhanced Shutdown Listener System:

   • Added a new shutdown listener mechanism in shutdown_listener.py that works better with Starlette/Uvicorn shutdown signals
   • Replaced the atexit handler with the new shutdown listener system
   • Added UUID-based listener registration and removal functionality

2. Docker Runtime Improvements:

   • Removed global _atexit_registered flag and stop_all_runtime_containers function
   • Added class-level _shutdown_listener_id to track the shutdown listener
   • Containers are now properly stopped when the application shuts down

3. Added Comprehensive Tests:

   • New test file test_shutdown_listener.py with thorough test coverage
   • Tests for listener registration, removal, and shutdown behavior
   • Tests for edge cases like removing listeners during shutdown

Technical Details

• The new shutdown listener system uses a dictionary to track listeners by UUID
• Signal handlers are properly chained to preserve existing handlers
• Listeners are called exactly once during shutdown
• Added safeguards against recursive shutdown calls

This change ensures that Docker containers are properly cleaned up when the application exits, preventing orphaned containers from consuming system resources.

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To run this PR locally, use the following command:

docker run -it --rm   -p 3000:3000   -v /var/run/docker.sock:/var/run/docker.sock   --add-host host.docker.internal:host-gateway   -e SANDBOX_RUNTIME_CONTAINER_IMAGE=docker.all-hands.dev/all-hands-ai/runtime:26f53e2-nikolaik   --name openhands-app-26f53e2   docker.all-hands.dev/all-hands-ai/openhands:26f53e2