Add the client-side subscriptions/listen driver (#3047)

docs_src/subscriptions/tutorial005.py

@@ -0,0 +1,20 @@
+import anyio
+
+from mcp import Client
+from mcp.client.subscriptions import SubscriptionLost
+
+from .tutorial003 import read_board
+
+
+async def keep_following(client: Client) -> None:
+    while True:
+        try:
+            async with client.listen(resource_subscriptions=["board://sprint"]) as sub:
+                print(await read_board(client))  # refetch: no replay across streams
+                async for _event in sub:
+                    print(await read_board(client))
+        except SubscriptionLost:
+            pass
+        # Either ending means the stream is gone. Back off before re-listening:
+        # a graceful close may be the server shedding load.
+        await anyio.sleep(1)