[Bug]: Align send_message signature for BaseClient and Client

[guglielmo-san]

What happened?

The current signature of the send_message method, differs from the Client interface

a2a-python/src/a2a/client/client.py

Lines 111 to 117 in d2d3860

	async def send_message(
	self,
	request: Message,
	*,
	context: ClientCallContext | None = None,
	request_metadata: dict[str, Any] | None = None,
	extensions: list[str] | None = None,

and the BaseClient implementation

a2a-python/src/a2a/client/base_client.py

Lines 62 to 69 in d2d3860

	async def send_message(
	self,
	request: Message,
	*,
	configuration: MessageSendConfiguration | None = None,
	context: ClientCallContext | None = None,
	request_metadata: dict[str, Any] | None = None,
	extensions: list[str] | None = None,

Relevant log output

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[Akshat8510]

I’d like to work on this.

Proposed Solution:
I will align the send_message signature in src/a2a/client/client.py with the BaseClient implementation by adding the configuration: MessageSendConfiguration | None = None keyword-only argument. I will also ensure that MessageSendConfiguration is correctly imported in the abstract class to maintain type-hint consistency.

Please assign this to me.