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

docs/assets/ts/artplayer-plugin-vtt-thumbnail.d.ts

@@ -1,10 +1,29 @@
-declare const artplayerPluginVttThumbnail: (option: { vtt?: string, style?: Partial<CSSStyleDeclaration> }) => (
-  art: Artplayer,
-) => {
-  name: 'artplayerPluginVttThumbnail'
+// Generated from the package public declaration by yarn build:ts. Do not edit.
+/* eslint-disable ts/no-redeclare -- Callable and public type namespace intentionally merge. */
+declare namespace artplayerPluginVttThumbnailDefinitions {
+  export interface Option {
+    vtt?: string
+    style?: Partial<CSSStyleDeclaration>
+  }
+  export interface Result {
+    name: 'artplayerPluginVttThumbnail'
+  }
+  /** Historical factory type. Actual registration is asynchronous. */
+  export type Factory = (option: Option) => (art: Artplayer) => Result
+  /** Accurate runtime view available without casts through the /runtime entry. */
+  export interface RuntimeFactory {
+    (option: Option): (art: Artplayer) => Promise<Result>
+    default: RuntimeFactory
+  }
+  /** Preserve historical extraction and replacement-function compatibility. */
+  export function artplayerPluginVttThumbnail(option: Option): (art: Artplayer) => Result
+}
+declare const artplayerPluginVttThumbnail: typeof artplayerPluginVttThumbnailDefinitions.artplayerPluginVttThumbnail
+declare namespace artplayerPluginVttThumbnail {
+  export type Option = artplayerPluginVttThumbnailDefinitions.Option
+  export type Result = artplayerPluginVttThumbnailDefinitions.Result
+  export type Factory = artplayerPluginVttThumbnailDefinitions.Factory
+  export type RuntimeFactory = artplayerPluginVttThumbnailDefinitions.RuntimeFactory
 }
-
-export default artplayerPluginVttThumbnail
-
 export = artplayerPluginVttThumbnail
 export as namespace artplayerPluginVttThumbnail;