Fix mypy errors in runtime/utils directory

[neubig]

This PR fixes all mypy errors in the openhands/runtime/utils directory. Changes include:

• Added missing return type annotations to functions
• Added missing type annotations to function parameters
• Fixed Any return type issues
• Added missing imports
• Fixed type compatibility issues with libtmux
• Added proper null checks for optional attributes

All changes are confined to the specified directory.

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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:977bbb3-nikolaik   --name openhands-app-977bbb3   docker.all-hands.dev/all-hands-ai/openhands:977bbb3