refactor(vtt-thumbnail): [PKG-VTT-THUMB-04] preserve legacy types and expose async runtime entry

refactor/fixtures/consumers/vtt-thumbnail-published.ts

@@ -0,0 +1,9 @@
+import Artplayer from 'artplayer'
+import vtt from 'artplayer-plugin-vtt-thumbnail'
+
+const option: Parameters<typeof vtt>[0] = { vtt: '/cues.vtt', style: { opacity: '0.8' } }
+const art = new Artplayer({ container: '#player', url: '/video.mp4', plugins: [vtt(option)] })
+const result: ReturnType<ReturnType<typeof vtt>> = { name: 'artplayerPluginVttThumbnail' }
+const replacement: typeof vtt = (_option: Parameters<typeof vtt>[0]) => (_art: Artplayer) => result
+void vtt(option)(art).name
+void replacement