Sovol Zero top feeder for 3× TPU printing speed

Simple design to relocate the spool on the top of the mini-printer with direct path to the extruder:

- lightweight structure held together by 4× M4x10 and 2× M4x18 screws (no nuts or heat set inserts needed)
- no-screwdriver necessary to remove the top bar to load/unload spool
- embedded PTFE lining to reduce friction
- new place for the filament runout sensor (also used as a filament constrain guide)
- optional, springy slide-on stops to keep the spool centered

With the new filament p