refactor(vtt-thumbnail): [PKG-VTT-THUMB-04] type runtime data and resource boundaries

packages/artplayer-plugin-vtt-thumbnail/src/request.ts

@@ -0,0 +1,23 @@
+import type { Lifetime } from './types'
+
+export default async function requestVtt(url = '', lifetime: Lifetime): Promise<string | void> {
+  if (lifetime.closed)
+    return
+  const controller = typeof AbortController === 'function' ? new AbortController() : null
+  const release = lifetime.own(() => controller?.abort())
+  try {
+    if (lifetime.closed)
+      return
+    const response = await lifetime.wait(controller ? fetch(url, { signal: controller.signal }) : fetch(url))
+    if (lifetime.closed)
+      return
+    if (response!.ok === false)
+      throw new Error(`Failed to fetch VTT thumbnails: HTTP ${response!.status}`)
+    if (lifetime.closed)
+      return
+    return await lifetime.wait(response!.text())
+  }
+  finally {
+    release()
+  }
+}