docs: add snippet verification for docs/ pages (#2115)

examples/snippets/clients/cancellation.py

@@ -0,0 +1,16 @@
+import mcp.types as types
+from mcp import ClientSession
+
+
+async def cancel_request(session: ClientSession) -> None:
+    """Send a cancellation notification for a previously-issued request."""
+    await session.send_notification(
+        types.ClientNotification(
+            types.CancelledNotification(
+                params=types.CancelledNotificationParams(
+                    requestId="request-id-to-cancel",
+                    reason="User navigated away",
+                )
+            )
+        )
+    )