feat: allow plugin.register to be used as a decorator

Author: pwwang

simplug.py

@@ -831,6 +831,10 @@ def register(self, *plugins: Any) -> None:
 
         self._batch_index += 1
 
+        if len(plugins) == 1 and callable(plugins[0]):
+            # allow to use as a decorator
+            return plugins[0]
+
     def get_plugin(self, name: str, raw: bool = False) -> object:
         """Get the plugin wrapper or the raw plugin object