refactor(mediabunny): [PKG-MB-04] isolate typed playback and readiness coordination

packages/artplayer-proxy-mediabunny/src/readiness.ts

@@ -0,0 +1,27 @@
+import type EventTarget from './EventTarget'
+
+export function publish(events: EventTarget, current: () => boolean, names: readonly string[]): void {
+  for (const name of names) {
+    if (!current())
+      return
+    events.emit(name)
+  }
+}
+
+export function metadataBarrier(ready: () => void, current: () => boolean) {
+  let video = false
+  let audio = false
+  let published = false
+  function complete(part: 'audio' | 'video'): void {
+    if (!current() || published)
+      return
+    if (part === 'video')
+      video = true
+    else audio = true
+    if (video && audio) {
+      published = true
+      ready()
+    }
+  }
+  return { video: () => complete('video'), audio: () => complete('audio') }
+}