Add typing to silence mypy untyped decorator

Author: T4rk1n

dash/_callback.py

@@ -77,7 +77,7 @@ def callback(
     cache_ignore_triggered=True,
     on_error: Optional[Callable[[Exception], Any]] = None,
     **_kwargs,
-):
+) -> Callable[..., Any]:
     """
     Normally used as a decorator, `@dash.callback` provides a server-side
     callback relating the values of one or more `Output` items to one or

dash/dash.py

@@ -1269,7 +1269,7 @@ def clientside_callback(self, clientside_function, *args, **kwargs):
             **kwargs,
         )
 
-    def callback(self, *_args, **_kwargs):
+    def callback(self, *_args, **_kwargs) -> Callable[..., Any]:
         """
         Normally used as a decorator, `@app.callback` provides a server-side
         callback relating the values of one or more `Output` items to one or