chore: drop google-genai from requirements

[haranrk]

adk-python includes google-genai in its dependency list

[DeanChensj]

@gemini-cli /review

[github-actions]

🤖 Hi @DeanChensj, I've received your request, and I'm working on it now! You can track my progress in the logs for more details.

[github-actions]

I've analyzed the PR and found that google-genai is still a required dependency for several modules in the codebase.

Specifically, S3ArtifactService and OpenMemoryService rely on google.genai.types for their public API and internal logic. Removing this dependency from pyproject.toml without refactoring those services will lead to ImportError at runtime and failures in the unit tests.

I recommend either:

1. Keeping the dependency if these services are intended to stay as-is.
2. Refactoring the services to remove their reliance on google-genai types before dropping the dependency.