performanceNodeTiming.idleTime
事件循环在事件循环的事件提供者（例如 epoll_wait）中空闲的时间量的高解析度毫秒时间戳。
这不考虑 CPU 使用率。
如果事件循环尚未开始（例如，在主脚本的第一个滴答中），则该属性的值为 0。
The high resolution millisecond timestamp of the amount of time the event loop
has been idle within the event loop's event provider (e.g. epoll_wait). This
does not take CPU usage into consideration. If the event loop has not yet
started (e.g., in the first tick of the main script), the property has the
value of 0.