Fix ci_max after new base-client release

[Marenz]

• Fix call of stream_method in latest base-client
• Add Mock for initial_metadata() for base-clients GrpcStreamer

[Copilot]

Pull Request Overview

This PR fixes compatibility issues with a new base-client release by updating the streaming interface and adding necessary mock functionality.

• Updates the StreamMicrogridDispatches method to return a mock stream object instead of an async iterator
• Removes unnecessary type casting in the client's stream method call
• Adds a _MockStream class to provide the initial_metadata() method required by the base-client's GrpcStreamer

Reviewed Changes

Copilot reviewed 2 out of 2 changed files in this pull request and generated 2 comments.

File	Description
src/frequenz/client/dispatch/test/_service.py	Adds _MockStream class and refactors StreamMicrogridDispatches to return mock stream object
src/frequenz/client/dispatch/_client.py	Removes type casting from stream method call to fix compatibility

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[Copilot]

The initial_metadata() method should return metadata instead of None to properly mock the gRPC interface. Consider returning an empty metadata object or the expected metadata type.

Suggested change

	async def initial_metadata(self) -> None:
	"""Do nothing, just to mock the grpc call."""
	_logger.debug("Called initial_metadata()")
	async def initial_metadata(self) -> list:
	"""Return empty metadata to mock the grpc call."""
	_logger.debug("Called initial_metadata()")
	return []

[Copilot]

[nitpick] The nested stream() function should be extracted to a separate method or moved outside the method to improve readability and maintainability.

[llucax]

Ah, interesting. Maybe other projects could be affected about this, if they didn't remove the casts after moving to use the proper async stub. 🤔

Once more life shows that there are no small or improbable breaking changes 😢

[llucax]

LGTM, but now that v0.11.1 is yanked, I would wait until we figure out why is this version failing before we merge this.