Function watch_tls_files 

async fn watch_tls_files(state: Arc<TlsReloadState>, debounce: Duration)

Watch the cert / key / client-CA files and call try_reload_tls after debounced changes. Mirrors the pattern in watcher.rs (parent-dir watch, debounce, then act). Runs until the channel closes; the caller drives shutdown by aborting the task that owns this future.