create PID helper class for running PID loops in a Mechanism's run method

[dejabot]

Description

Thought exercise to simplify running PID loops in a Mechanism's run method.
PIDRunner handles:

• calling a Motor's set method iff this is the first call, if the setpoint, slot, or feedforward have changed.
• uses functional interfaces to get the setpoint, output, slot, or feedforward. makes it simple for callers to specify them, eg via method references
• provides default implementations for common approaches to picking the slot, computing feedforward

How Has This Been Tested?

Needs to be tested. Sending for early feedback.

• Unit tests: [Add your description here]
• Simulator testing: [Add your description here]
• On-robot bench testing: [Add your description here]
• On-robot field testing: [Add your description here]

[rcahoon]

FYI, for arbitraryFeedForward strategies based on sensors (e.g. cosineArbitraryFeedForward), the value will likely change on every evaluation

[dejabot]

thx! q - wouldn't it stop once the mechanism stopped moving? or would there be unintended micromovements, eg from vibrations, etc.

in that case, wdyt of using a minimum change threshold?

[rcahoon]

yes. in addition, many sensors will have signal noise that results in different measurements, even if the mechanism is perfectly still.

a change threshold is probably fine. i would think at most 0.01, unless you want to make it configurable