feat: add a manual cli for testing proxy

[awsjjzhou]

Summary

Changes

Add a manual CLI testing tool to easily test the whole flow: client -> proxy -> mcp server

User experience

User can run e.g. uv run python -m tests.integ.manual_test --endpoint https://my-endpoint.com --service bedrock --region us-west-2 --list-tools for testing end2end.

"--list-tools" can be further extended to call tools in future

Checklist

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• I have reviewed the contributing guidelines
• I have performed a self-review of this change
• Changes have been tested
• Changes are documented

Is this a breaking change? (Y/N)

• Yes
• No

Please add details about how this change was tested.

• Did integration tests succeed?
• If the feature is a new use case, is it necessary to add a new integration test case?

Acknowledgment

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[awsjjzhou]

Holding this for now since @JacquesPotgieter is working on a mcp-inspector script for a similar testing purpose

[awsjjzhou]

Closing this since it's temporarily not needed anymore