refresh_physics library Null safety


a scrollPhysics for config refresh scroll effect,enable viewport out of edge whatever physics it is in ClampingScrollPhysics, it doesn't allow to flip out of edge,but in RefreshPhysics,it will allow to do that, by parent physics passing,it also can attach the different of iOS and Android different scroll effect it also handles interception scrolling when refreshed, or when the second floor is open and closed. with SpringDescription passing,you can custom spring back animate,the more paramter can be setting in RefreshConfiguration