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

src/a2a/client/client.py

@@ -3,10 +3,13 @@
 
 from abc import ABC, abstractmethod
 from collections.abc import AsyncIterator, Callable, Coroutine
+from types import TracebackType
 from typing import Any
 
 import httpx
 
+from typing_extensions import Self
+
 from a2a.client.middleware import ClientCallContext, ClientCallInterceptor
 from a2a.client.optionals import Channel
 from a2a.types import (
@@ -107,6 +110,19 @@ def __init__(
         self._consumers = consumers
         self._middleware = middleware
 
+    async def __aenter__(self) -> Self:
+        """Enters the async context manager."""
+        return self
+
+    async def __aexit__(
+        self,
+        exc_type: type[BaseException] | None,
+        exc_val: BaseException | None,
+        exc_tb: TracebackType | None,
+    ) -> None:
+        """Exits the async context manager and closes the client."""
+        await self.close()
+
     @abstractmethod
     async def send_message(
         self,
@@ -209,3 +225,7 @@ async def consume(
             return
         for c in self._consumers:
             await c(event, card)
+
+    @abstractmethod
+    async def close(self) -> None:
+        """Closes the client and releases any underlying resources."""