The code to recalculate the uptime to walltime adjustment was broken
(e.g. the longer we leave it after reboot the more inaccurate the time
setting becomes).
Fixes: 80079e4 ("wasp: nrf_rtc: Add a tiny bit of extra resolution")
We now have a couple of applications (stopwatch, Game of Life) that benefit
from sub-second precision. The micropython RTC/utime code for nrf still
needs a major overhaul but this allows us to paper over the cracks for
just a little longer.
Currently this supports time only (no date) and it based on the
RTCounter class which is customized for nRF ports. At present
the nRF port doesn't have proper machine.rtc support so we have
implemented within wasp instead.
