Timestamp improvements

[ItsHarper]

1. All returned timestamps should be defined in the same unit and reference frame as WPILib's CAN timestamps
   1. WPILib doesn't do a fantastic job of being consistent and documenting how timestamps work. Improve this upstream, and make sure that the behavior is consistent between simulation and the roboRIO.
2. All timestamp values should have a type of uint64_t
   1. WPILib HAL timestamps are typed as uint32_t, unfortunately. We'll need to use CANMessage for our internal CAN stream data representation, rather than the WPILib version like we do now.