🛠️ Ruff errors refactored.

tidal_dl_ng/helper/decorator.py

@@ -1,3 +1,6 @@
+from typing import ClassVar
+
+
 class SingletonMeta(type):
     """
     The Singleton class can be implemented in different ways in Python. Some
@@ -5,7 +8,7 @@ class SingletonMeta(type):
     metaclass because it is best suited for this purpose.
     """
 
-    _instances = {}
+    _instances: ClassVar[dict] = {}
 
     def __call__(cls, *args, **kwargs):
         """