ET4 Simple Fan Duct

Simple quick fan duct. This replaces the stock fan duct and reuses the screws.

I wanted something simple to print and to attach using all of the original parts. This works as well as the other ducts. But this one allows me to:
- keep the silicon sock on the heater block
- replace nozzle without removing the duct
- easier to clean around the nozzle
- tapered and spaced far enough to not get melted by the heat block
- doesn't blow on the nozzle, so the hotend maintains a more constant temp without an enclosure.

This will need to be printed in something that can resist heat. I used PETG, but I think Nylon, ASA, PC, and ABS would work as well.