Prusa MK3 Bear Full Upgrade length-adjustable X idler

Rework of the stock MK3 R3 X idler which allows +/- 1mm of rod length adjustment. The final length is locked in place using two M3x8 screws.

Only valuable for custom builds, such as the full bear upgrade. This is unlikely to be useful for the plain MK3 or the bear half-upgrade.

I noticed the Z screws were simultaneously flexing in opposing directions when going full up or down, a sign of rod-length mismatch for your assembly. Note: if they displace in random directions then rod-length is *