+ /**
+ * Finds the last free worker node key based on the number of tasks the worker has applied.
+ *
+ * If a worker is found with `0` running tasks, it is detected as free and its worker node key is returned.
+ *
+ * If no free worker is found, `-1` is returned.
+ *
+ * @returns A worker node key if there is one, `-1` otherwise.
+ */
+ findLastFreeWorkerNodeKey: () => number