Fix Track model to match Python reference

- R128: changed from JSONR128 float64 to R128 struct with i, tp, important_secs fields
  (Python R128 is an object, not a number)
- StorageID -> StorageDir with json tag storage_dir (Python API uses storage_dir)
- Lyrics: replaced TrackLyricsInfo with Lyrics (from supplement/lyrics.py) and
  TrackLyricsInfo (from track/lyrics_info.py with has_available_sync_lyrics,
  has_available_text_lyrics fields)
- Track.Lyrics field now maps to lyrics_info JSON key with TrackLyricsInfo type

internal/models/track_test.go

@@ -43,7 +43,7 @@ func TestTrack_DeJSON(t *testing.T) {
 		"id": "123",
 		"title": "Test Track",
 		"duration_ms": 180000,
-		"storage_id": "456",
+		"storage_dir": "456",
 		"cover_uri": "https://example.com/cover.jpg",
 		"genre": "rock",
 		"version": "album",
@@ -55,7 +55,7 @@ func TestTrack_DeJSON(t *testing.T) {
 		"artists": [{"id": "1", "name": "Artist 1", "cover_uri": "https://example.com/artist.jpg"}],
 		"albums": [{"id": "789", "title": "Test Album", "cover_uri": "https://example.com/album.jpg", "year": 2023}],
 		"major": {"id": "major1", "name": "Major Label", "description": "Big label"},
-		"lyrics": {"id": "lyr1", "text": "Test lyrics", "available": true, "has_text": true}
+		"lyrics_info": {"has_available_sync_lyrics": true, "has_available_text_lyrics": true}
 	}`)
 
 	track := &Track{BaseModel: *NewBaseModel(client)}
@@ -80,8 +80,8 @@ func TestTrack_DeJSON(t *testing.T) {
 	if resultTrack.Major == nil || resultTrack.Major.Name != "Major Label" {
 		t.Errorf("Expected Major 'Major Label'")
 	}
-	if resultTrack.Lyrics == nil || resultTrack.Lyrics.Text != "Test lyrics" {
-		t.Errorf("Expected Lyrics 'Test lyrics'")
+	if resultTrack.LyricsInfo == nil || resultTrack.LyricsInfo.HasAvailableSyncLyrics != true {
+		t.Errorf("Expected LyricsInfo.HasAvailableSyncLyrics true")
 	}
 }