use len of parameters to check progress variant, can't rely on clients naming params consistently

Author: davemssavage

src/mcp/shared/session.py

@@ -274,7 +274,7 @@ async def send_request(
             # note this is required to ensure backwards compatibility
             # for previous clients
             signature = inspect.signature(progress_callback.__call__)
-            if "resource_uri" in signature.parameters:
+            if len(signature.parameters) == 3:
                 # Store the callback for this request
                 self._resource_callbacks[request_id] = progress_callback  # type: ignore
             else: