feat(client): expose close() and async context manager support on abstract Client (lint)

Author: cchinchilla-dev

src/a2a/client/client.py

@@ -6,10 +6,10 @@
 from types import TracebackType
 from typing import Any
 
-from typing_extensions import Self
-
 import httpx
 
+from typing_extensions import Self
+
 from a2a.client.middleware import ClientCallContext, ClientCallInterceptor
 from a2a.client.optionals import Channel
 from a2a.types.a2a_pb2 import (
@@ -236,4 +236,4 @@ async def consume(
 
     @abstractmethod
     async def close(self) -> None:
-        """Closes the client and releases any underlying resources."""
+        """Closes the client and releases any underlying resources."""