feat: add total duration for playlist

app/Http/Controllers/MusicCategoryController.php

@@ -126,7 +126,7 @@ public function grouped($id)
                     'description' => $sub->description,
                     'image_url' => $sub->image?->url,
                 ],
-                'playlists' => $sub->playlists,
+                'playlists' => $sub->playlists->each(fn ($p) => $p->append('duration')),
             ])->values(),
         ]);
     }

app/Http/Controllers/MusicPlaylistController.php

@@ -98,6 +98,8 @@ public function show($id)
                 ->latest()
                 ->paginate(15);
             
+            $playlist->append('duration');
+
             return response()->json(array_merge(
                 $playlist->toArray(),
                 [

app/Models/MusicPlaylist.php

@@ -71,4 +71,10 @@ public function getTotalDurationAttribute()
     {
         return $this->musics()->where('music.is_active', true)->sum('music.duration');
     }
+
+    // Total play time of the playlist = sum of its active musics' durations.
+    public function getDurationAttribute()
+    {
+        return $this->total_duration;
+    }
 }