Function start_heartbeat 

pub fn start_heartbeat(
    client: Client,
    server: String,
    token: Option<String>,
    heartbeat_state: HeartbeatState,
    processing: Arc<Mutex<HashSet<String>>>,
    cognition_config: CognitionHeartbeatConfig,
) -> JoinHandle<()>

Start the heartbeat background task Returns a JoinHandle that can be used to cancel the heartbeat