Improve typing of `decorator.decoratorx`

I do not have capacity to open a PR for this, but I would like to suggest the following improvement to decorator.decoratorx which type-checks fine wherever I use it:

class _DecoratorX(Protocol):
    def __call__(
        self, caller: Callable[Concatenate[Callable[_P, _T], _P], _T]
    ) -> Callable[[Callable[_P, _T]], Callable[_P, _T]]: ...

decoratorx: _DecoratorX

在 typeshed 仓库中搜索 decorator.decoratorx 的声明，并检查其周围的存根。将当前的类型标注与提议的 _DecoratorX 协议进行比较，然后运行相关的静态类型检查，以确认改进后的注解能够正常工作且不会引入回归。