Implement inverse kinematics for 2-DOF arm (shoulder + elbow)

[bacemkarray]

Replace direct angle splitting with a proper inverse kinematics (IK) module for the 2-DOF planar arm (shoulder+ elbow).

Currently, the send_y value is split linearly between the two joints. A basic solution but rudimentary.

[bacemkarray]

This issue is currently a low priority.