Previously, we used `useLiveData(guardService.can$())` to get the guard result, but `guardService.can$()` will request the server to revalidate the permission when calling it, will cause additional network requests when re-render.
This pr make a new hook `useGuard` to fix this problem.
And the side effect in `can$` is moved to `revalidateCan()` to make that the subscribe method is pure