Use flow rates instead of integrals in backend. This allows us to delay
the data to the mitpoint integration time and simplifies the code in
general.
Gyro compensation can still be done in EKF2 if needed, but the
flow module normally already appends the correct gyro data to the flow
message.
- EKF isTimedOut(), isRecent(), and isNewestSampleRecent() need to handle the case where the timestamp has never been set
- reset() more thoroughly reset fields (mainly impacts unit tests)
- refactor all EKF backend output predictor pieces into new OutputPredictor class
- output states are now calculated immediately with new high rate IMU rather than after EKF update
- IMU delayed sample is passed as around as control data to avoid storing an extra copy and make the requirement clear
bresch