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/util.py

@@ -343,8 +343,7 @@ def fetch_url(url, headers=(), timeout=15, report_text=None, data=None,
                     and debug_name is not None
                     and content):
                 save_dir = os.path.join(settings.data_dir, 'debug')
-                if not os.path.exists(save_dir):
-                    os.makedirs(save_dir)
+                os.makedirs(save_dir, exist_ok=True)
 
                 with open(os.path.join(save_dir, debug_name), 'wb') as f:
                     f.write(content)
@@ -902,8 +901,7 @@ INNERTUBE_CLIENTS = {
 def get_visitor_data():
     visitor_data = None
     visitor_data_cache = os.path.join(settings.data_dir, 'visitorData.txt')
-    if not os.path.exists(settings.data_dir):
-        os.makedirs(settings.data_dir)
+    os.makedirs(settings.data_dir, exist_ok=True)
     if os.path.isfile(visitor_data_cache):
         with open(visitor_data_cache, 'r') as file:
             print('Getting visitor_data from cache')