ARC left back top with magnet holes for ptfe splitter

Added magnet base connection point for a PTFE AMS/external spool splitter with 6x3mm magnets. Since the ARC causes the outer shell to no longer be magnetic, I wanted to have a good way of attaching the PTFE splitter to the rear of the case without further increasing the thickness of the mounting point to keep it aligned with where the PTFE tube exits the case. (V2 is the correct side, original was the opposite corner, oops!) Acrylic panel set now available in my Etsy shop! https://www.etsy.com/listing/1394686261/acrylic-panel-set-for-bambu-p1p-arc