Camera Update Callback

[dhyces]

This callback is a simple implementation for a callback after the Camera#update method is called from the WorldRenderer. The mixin itself is rather trivial, though due to the nature of rendering code (changing values to get it just right and hotswapping), it requires a public static method outside of the mixin class when not using mixin hotswap. The included test slowly rotates the camera upward when the player sleeps in a bed.