Fix stop button functionality

[neubig]

This PR is aiming to fix the stop button functionality #6848

It

• refactors bash command processing
• adds a new method get_running_processes() to the BashSession class.

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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:92b919c-nikolaik   --name openhands-app-92b919c   docker.all-hands.dev/all-hands-ai/openhands:92b919c