* feat(bc): implement timekeeping
* fix(time): Milliseconds and Seconds return storage should be 64-bit
* fix(time): nsec should be explicitly cast to uint32
* test(time): rudimentary tests for timekeeping
* fix(time): check properly for timestamp + nsec overflows in MakeTime and BreakTime
* fix(time): include UNIX time headers on Mac, too
* test(time): test can tolerate system hiccups