Fix the OpenTelemetry parent-span behavior for Node.js Middleware. `Middleware.execute` currently inherits `BaseServer.handleRequest` as its parent, unlike Middleware in the Edge runtime. Make `Middleware.execute` and `BaseServer.handleRequest` sibling spans: when there is no incoming propagated trace context, both must be root spans; when an incoming trace context is present, both must be direct children of that incoming span and remain in its trace. Preserve existing middleware request handling and Edge runtime behavior.