MK3S+ Extruder Idler Upgrade

This version of the idler was inspired by @MihaiDesigns_9605 work to root cause inconsistent extrusion as outlined in his investigation found here. 

I've been printing with this idler for a few months on my two MK3S+'s and have noticed an improvement in the print quality.  The idler is a quick print using PRUSA's recommended print settings for their replacement parts and a 5min retrofit if you'd like to try it out. 

The implementation is not perfect but I was looking to make it simple and effective with minimal impact to retrofitting a stock extruder.  As noted in Mihai's investigation, not all printers exhibit the wood grain pattern he talks about so your mileage may vary.

What was changed:

Starting with the original idler geometry, I increased the clearance to the extruder body to give it a bit more freedom to move.

 I then modified the hole for the idler hinge to be a slot and added an internal pivot point to be in line with the filament path.  With the tension screw in between the gears and filament path, this effectively pivots the idler around the filament and always keeps the gears meshed. 

[Update 5/12/23]

Added MMU2S idler for MK3S+ and Bear Extruder (MK3) pulley adaptation.  I don't have any of these configurations and can't confirm fit so let me know of any issues.