Anycubic i3 Mega partfan monstrosity

Boxy, but good (enough).
- Includes a part that is effectively a remix of: https://www.thingiverse.com/thing:2479809
- Borrows dimensions between fixing bolts from: https://www.thingiverse.com/thing:2457516
- This is an attempt to get partfan coverage from both/all sides, while retaining the original plate mount to the bearings. After several attempts I gave up in disgust with the quest to design something elegant, and just settled for monstrous and temporary: I am a little bit over trying to modify the mega's existing hotend, so this is simply a temporary means of getting better part cooling while I print components for an entirely different printer.
- I may eventually revise this later, but it will likely be in a version that completely replaces the megas hotend compartment right back to the X carriage bearings.
- It's not pretty, and despite having a COD LED inside it to illuminate the nozzle it's almost impossible to see underneath the ducts anyway, and the LED reaaaaaly needs