refactor: update export syntax to default for multiple plugins and adjust package.json formatting

packages/artplayer-plugin-multiple-subtitles/types/artplayer-plugin-multiple-subtitles.d.ts

@@ -1,8 +1,5 @@
 import type Artplayer from 'artplayer'
 
-export = artplayerPluginMultipleSubtitles
-export as namespace artplayerPluginMultipleSubtitles;
-
 declare const artplayerPluginMultipleSubtitles: (option: {
   subtitles: {
     url?: string
@@ -14,3 +11,5 @@ declare const artplayerPluginMultipleSubtitles: (option: {
 }) => (art: Artplayer) => {
   name: 'multipleSubtitles'
 }
+
+export default artplayerPluginMultipleSubtitles