no-service-found warning should actually check if there is any service not just operations

[timotheeguerin]

https://azure.github.io/typespec-azure/playground/?e=%40azure-tools%2Ftypespec-autorest&c=aW1wb3J0ICJAYXp1cmUtdG9vbHMvdHlwZXNwZWMtxhVjb3JlIjsKCkBzZXJ2aWNlKCN7IHRpdGxlOiAiQcQiIEFJIiB9KQpuYW1lc3BhY2UgxRcuQUkuUHJvamVjdHMgewoKfQo%3D&options=%7B%7D&vs=%7B%7D

import "@azure-tools/typespec-azure-core";

@service
namespace Test;

Additionally it would be good that the error is not flagged on all namespaces, maybe only on user namespaces