refactor audio to use custom listener stores

src/lib/audio/episode-details.ts

@@ -0,0 +1,5 @@
+import { writable } from 'svelte/store';
+
+export type EpisodeDetails = Record<string, string | number | boolean> | null;
+export const episode_details = writable<EpisodeDetails>(null);
+export type EpisodeDetailsStore = typeof episode_details;