image: properly handle uniqueness of non-embedded covers

Use a UID instead. This is non-ideal but all we can do.

app/src/main/java/org/oxycblt/auxio/image/extractor/Components.kt

@@ -27,7 +27,7 @@ import javax.inject.Inject
 
 class CoverKeyer @Inject constructor() : Keyer<Collection<Cover>> {
     override fun key(data: Collection<Cover>, options: Options) =
-        "${data.map { it.perceptualHash }.hashCode()}"
+        "${data.map { it.uniqueness }.hashCode()}"
 }
 
 class CoverFetcher

app/src/main/java/org/oxycblt/auxio/image/extractor/Cover.kt

@@ -20,6 +20,7 @@ package org.oxycblt.auxio.image.extractor
 
 import android.net.Uri
 import org.oxycblt.auxio.list.sort.Sort
+import org.oxycblt.auxio.music.Music
 import org.oxycblt.auxio.music.Song
 
 /**
@@ -31,14 +32,20 @@ import org.oxycblt.auxio.music.Song
  *   an album cover.
  * @author Alexander Capehart (OxygenCobalt)
  */
-data class Cover(val perceptualHash: String?, val mediaStoreUri: Uri, val songUri: Uri) {
+data class Cover(val uniqueness: Uniqueness?, val mediaStoreUri: Uri, val songUri: Uri) {
+    sealed interface Uniqueness {
+        data class PerceptualHash(val perceptualHash: String) : Uniqueness
+
+        data class UID(val uid: Music.UID) : Uniqueness
+    }
+
     companion object {
         private val FALLBACK_SORT = Sort(Sort.Mode.ByAlbum, Sort.Direction.ASCENDING)
 
         fun order(songs: Collection<Song>) =
             FALLBACK_SORT.songs(songs)
                 .map { it.cover }
-                .groupBy { it.perceptualHash }
+                .groupBy { it.uniqueness }
                 .entries
                 .sortedByDescending { it.value.size }
                 .map { it.value.first() }

app/src/main/java/org/oxycblt/auxio/music/device/DeviceMusicImpl.kt

@@ -114,7 +114,11 @@ class SongImpl(
         get() = _genres
 
     override val cover =
-        Cover(rawSong.coverPerceptualHash, requireNotNull(rawSong.mediaStoreId).toCoverUri(), uri)
+        Cover(
+            rawSong.coverPerceptualHash?.let { Cover.Uniqueness.PerceptualHash(it) }
+                ?: Cover.Uniqueness.UID(uid),
+            requireNotNull(rawSong.mediaStoreId).toCoverUri(),
+            uri)
 
     /**
      * The [RawAlbum] instances collated by the [Song]. This can be used to group [Song]s into an