Fix mypy errors in events directory

[neubig]

This PR fixes all mypy errors in the openhands/events directory. The changes include:

• Added proper type annotations to functions and methods
• Fixed issues with Any vs any
• Added proper type checking for getattr() calls
• Fixed string concatenation with dict
• Added proper null checks for optional values
• Fixed lambda type inference issues
• Added proper type assertions for returned values

All changes are confined to the openhands/events directory.

Part of #6809

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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:7a37d99-nikolaik   --name openhands-app-7a37d99   docker.all-hands.dev/all-hands-ai/openhands:7a37d99