Tusk cooling for Duet smart effector

The [Duet Smart Effector](https://duet3d.com/wiki/Smart_effector_and_carriage_adapters_for_delta_printer) is a nice upgrade to a plastic effector. Nozzle-based probing, guaranteed-precise dimensions, built-in lights, and easy-to-detach cables. However, the provided 40mm fan shroud didn't seem to generate enough cooling with the 40mm fan I had, and axial fans aren't known to be great for part cooling anyway.

I saw the [Tusk fan shroud blog](http://www.sublimelayers.com/2017/03/the-tusk-fan-sh