fix: include null id in JSON-RPC invalid request error responses and add validation tests

mempalace/mcp_server.py

@@ -1969,7 +1969,7 @@ SUPPORTED_PROTOCOL_VERSIONS = [
 
 def handle_request(request):
     if not isinstance(request, dict):
-        return {"jsonrpc": "2.0", "error": {"code": -32600, "message": "Invalid Request"}}
+        return {"jsonrpc": "2.0", "id": None, "error": {"code": -32600, "message": "Invalid Request"}}
     method = request.get("method") or ""
     params = request.get("params") or {}
     req_id = request.get("id")