refactor: 必要时取消定时器，提高性能

src/chrome/content-script.cjs

@@ -6,14 +6,12 @@ const getVideoElement = () => {
   return videoWrapper.querySelector('video')
 }
 
-var danmukuBoxLoaded = false
-setInterval(function () {
-  if (danmukuBoxLoaded) return
+let danmukuBox = null
+const timerIframe = setInterval(function () {
+  if (danmukuBox) return clearInterval(timerIframe)
 
-  var danmukuBox = document.getElementById('danmukuBox')
+  danmukuBox = document.getElementById('danmukuBox')
   if (danmukuBox) {
-    danmukuBoxLoaded = true
-    setTimeout(function () {
     var vKey = ''
     for (const key in danmukuBox?.dataset) {
       if (key.startsWith('v-')) {
@@ -32,7 +30,6 @@ setInterval(function () {
     }
     //insert before first child
     danmukuBox?.insertBefore(iframe, danmukuBox?.firstChild)
-    }, 1500)
   }
 }, 1000)