Add client handling for sampling, list roots, ping (#218)

Adds sampling and list roots callbacks to the ClientSession, allowing the client to handle requests from the server.

Co-authored-by: TerminalMan <84923604+SecretiveShell@users.noreply.github.com>
Co-authored-by: David Soria Parra <davidsp@anthropic.com>

README.md

@@ -476,9 +476,21 @@ server_params = StdioServerParameters(
     env=None # Optional environment variables
 )
 
+# Optional: create a sampling callback
+async def handle_sampling_message(message: types.CreateMessageRequestParams) -> types.CreateMessageResult:
+    return types.CreateMessageResult(
+        role="assistant",
+        content=types.TextContent(
+            type="text",
+            text="Hello, world! from model",
+        ),
+        model="gpt-3.5-turbo",
+        stopReason="endTurn",
+    )
+
 async def run():
     async with stdio_client(server_params) as (read, write):
-        async with ClientSession(read, write) as session:
+        async with ClientSession(read, write, sampling_callback=handle_sampling_message) as session:
             # Initialize the connection
             await session.initialize()