Inconsistent servo mount orientation on Piper-Leader-Arm upper_arm causes cable routing problem #39

The servo mount orientation of the upper_arm part does not match the servo mount orientation of the lower_arm part on the Piper-Leader-Arm.
This mismatch forces the servo bus cable to route around the upper_arm to serially connect the two servos. The 20cm servo bus cable is too short for this routing path, and the cable is prone to tangling during operation.

I have completed 3D modeling optimization for the servo mount of the upper_arm part. The optimized mount allows the servo motor to be installed in arbitrary orientations. With this change, the 20cm servo bus cable is long enough to connect the two servos on these parts, and the cable routing becomes safer. I will submit a corresponding PR with the optimized STL file for this improvement.