Function run_config_reload_worker_with_observer 

pub async fn run_config_reload_worker_with_observer<N, F, Fut>(
    notifier: Arc<N>,
    config: ConfigReloadWorkerConfig,
    shutdown: CancellationToken,
    reload: F,
    observer: Option<&dyn ConfigReloadObserver>,
) -> Result<()>
where
    N: ConfigChangeNotifier + ?Sized,
    F: FnMut(ConfigReloadMessage) -> Fut,
    Fut: Future<Output = Result<()>>,

Runs a reload subscription loop and reports low-cardinality observations.