Adds TimeBase.h/cpp with ClockOffset (latched wall-clock offset with
one-sided recalibration on positive drift only, so early-arriving packets
do not wobble the trace) and HrtRateFit (sliding-window OLS that recovers
an unknown hrt tick rate from receive timestamps). Also adds
TimeSignalScale() which maps UDPS type codes to seconds-per-count.
9 new tests, all 28 pass.
Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>
