turn processTx into a template method

[GrayHoang]

Description of the task

In stspin_motor_controller.h:
Instead of using std::variant and visitor in processTx, consider turning processTx into a template method with frame type as a template param, and use template specialization to select implementation based on frame type

Acceptance criteria

• No longer a std::variant and visitor in processTx

Blocked By

[adrianchan787]

populateTx not processTx