fix(client): align send_message signature with BaseClient

Signed-off-by: Akshat Kumar <akshat230405@gmail.com>

Author: Akshat8510

src/a2a/client/client.py

@@ -18,6 +18,7 @@
     ListTasksRequest,
     ListTasksResponse,
     Message,
+    SendMessageConfiguration,
     PushNotificationConfig,
     StreamResponse,
     SubscribeToTaskRequest,
@@ -111,6 +112,7 @@ async def send_message(
         self,
         request: Message,
         *,
+        configuration: SendMessageConfiguration | None = None,
         context: ClientCallContext | None = None,
         request_metadata: dict[str, Any] | None = None,
         extensions: list[str] | None = None,