Extract wheel encoder to separate thread for faster sampling

[taesungh]

Similar to last year's process_encoder.py, the wheel encoder will not be sampled at a sufficient speed through the normal FSM tick: sensor measurements from I2C will take more than 10 ms whereas the wheel encoder needs to be sampled at around 1.5 ms for the pod's top speed of about 20 mph.

• Explore options for multiprocessing which won't be limited to a single process
  • Tokio's multi-thread scheduler might be sufficient on its own to have the wheel encoder task run on a dedicated process
• Instead of measuring the wheel encoder in running_periodic spawn a new task in StateMachine::run which runs its own loop to sample the wheel encoder at a faster rate than the standard FSM tick