fix: race condition in os.makedirs causing worker crashes

Replace check-then-create pattern with exist_ok=True to prevent
FileExistsError when multiple workers initialize simultaneously.

Affects:
- subscriptions.py: open_database()
- watch.py: save_decrypt_cache()
- local_playlist.py: add_to_playlist()
- util.py: fetch_url(), get_visitor_data()
- settings.py: initialization

Fixes Gunicorn worker startup failures in multi-worker deployments.

youtube/watch.py

@@ -329,11 +329,8 @@ def get_ordered_music_list_attributes(music_list):
 
 
 def save_decrypt_cache():
-    try:
-        f = open(os.path.join(settings.data_dir, 'decrypt_function_cache.json'), 'w')
-    except FileNotFoundError:
-        os.makedirs(settings.data_dir)
-        f = open(os.path.join(settings.data_dir, 'decrypt_function_cache.json'), 'w')
+    os.makedirs(settings.data_dir, exist_ok=True)
+    f = open(os.path.join(settings.data_dir, 'decrypt_function_cache.json'), 'w')
 
     f.write(json.dumps({'version': 1, 'decrypt_cache':decrypt_cache}, indent=4, sort_keys=True))
     f.close()