message: fix: set lastSentAt on each heartbeat
diff: @@ -49,6 +49,7 @@ export async function heartbeat(gateway: GatewayManager, shardId: number, interv
  if (currentShard.ws.readyState !== WebSocket.OPEN) return;
  currentShard.heartbeat.acknowledged = false;
  + currentShard.heartbeat.lastSentAt = Date.now();
  currentShard.ws.send(
  JSON.stringify({
  