2980a343c1
Wire AuthService into NatsServer and NatsClient to enforce authentication on incoming connections. The server builds an AuthService from NatsOptions, sets auth_required in ServerInfo, and generates per-client nonces when NKey auth is configured. NatsClient validates credentials in ProcessConnect, enforces publish/subscribe permissions, and implements an auth timeout that closes connections that don't send CONNECT in time. Existing tests without auth continue to work since AuthService.IsAuthRequired is false by default.