fix: Add missing type annotations in utils/ directory

[neubig]

This PR adds missing type annotations to files in the utils/ directory:

• Added return type annotations to all functions in prompt.py
• Added parameter and return type annotations to methods in http_session.py
• Added return type annotations to all functions in shutdown_listener.py
• Fixed the return type in tenacity_stop.py by explicitly casting to bool

All mypy checks now pass for the utils directory.

Part of #6397

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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:30c441d-nikolaik   --name openhands-app-30c441d   docker.all-hands.dev/all-hands-ai/openhands:30c441d

[neubig]

Note: this is necessary because it is used, e.g. in this file:
openhands/runtime/builder/remote.py