add ruff format, ruff check, time_picker, project structure and imports reorganized

model/_singleton.py

@@ -1,6 +1,7 @@
 class Singleton(type):
     _instances = {}
+
     def __call__(cls, *args, **kwargs):
         if cls not in cls._instances:
             cls._instances[cls] = super(Singleton, cls).__call__(*args, **kwargs)
-        return cls._instances[cls]
+        return cls._instances[cls]