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

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

@@ -0,0 +1,7 @@
+import type { Thumbnail } from './types'
+import parseVtt from './parseVtt'
+
+// Preserve the historical source helper while registration owns its requests.
+export default async function getVttArray(vttUrl = ''): Promise<Thumbnail[]> {
+  return parseVtt(await (await fetch(vttUrl)).text(), vttUrl)
+}