Time: leap seconds and TAI

[damip]

Check the monotonicty and leaping of our timestamp.

https://man7.org/linux/man-pages/man3/clock_gettime.3.html

              The CLOCK_MONOTONIC clock is not affected by discontinuous
              jumps in the system time (e.g., if the system administrator
              manually changes the clock), but is affected by the incremen‐
              tal adjustments performed by [adjtime(3)](https://man7.org/linux/man-pages/man3/adjtime.3.html) and NTP.  This clock
              does not count time that the system is suspended.  All
              CLOCK_MONOTONIC variants guarantee that the time returned by
              consecutive calls will not go backwards, but successive calls
              may—depending on the architecture—return identical (not-
              increased) time values.

• are there any forbidden timestamp values that might make us panic ?
• what happens on non-monotonic hops ? can they happen at all ? can it trigger the same timer twice ? is it a problem ?
• study alternatives: for example TAI: https://en.wikipedia.org/wiki/International_Atomic_Time