fix evil edge case (and fix typo)

is it really my fault. they say it's required right here: https://developer.apple.com/documentation/applemusicapi/songs/attributes-data.dictionary

src/appleMusicApi/types/attributes.ts

@@ -53,7 +53,9 @@ export type SongAttributes<
     composerName?: string;
     contentRating?: string;
     discNumber?: number;
-    durationInMillis: number;
+    // >claims to be required
+    // >not present sometimes ??
+    durationInMillis?: number;
     editorialNotes?: EditorialNotes;
     genreNames: string[];
     hasLyrics: boolean;

src/index.ts

@@ -16,7 +16,7 @@ setGlobalDispatcher(new Agent().compose([
     // TODO: configurable cache sizes?
     // these values are pretty nice for non-binary (lol) data
     interceptors.cache({ store: new cacheStores.MemoryCacheStore({
-        maxSize: 50 * 1024 * 1024, // 5mb
+        maxSize: 50 * 1024 * 1024, // 50mb
         maxCount: 1000,
         maxEntrySize: 5 * 1024 // 5kb
     })})

src/web/index.ts

@@ -24,7 +24,7 @@ const hbs = create({
     helpers: {
         add(a: number, b: number) { return a + b; },
         arrayJoin(array: string[], separator: string) { return array.join(separator); },
-        formatDuration(duration: number) { return formatDuration(duration); },
+        formatDuration(duration?: number) { return duration === undefined ? "n/a" : formatDuration(duration); },
         greaterThan(a: number, b: number) { return a > b; },
         mapNumberToLetter(num: number) { return String.fromCharCode(num + 64); } // A = 1, B = 2
     }