Ender 3 polyvalent hot end fan mount / pen holder

This is a replacement for the original metal cube that holds the heat sink fan and part cooling fan. It uses the original fans and screws. It brings several improvements compared to the original part:
- The heat sink air flow is completely directed to the top, with no air flowing on the heat block and printed part. This improves ABS printing, making stronger parts
- Noise reduction: the heat sink fan is suspended by thin flexible joins to reduce the transmission of vibration
- Better visibili