Rework Time management helpers

To clarify the usage of each API split in two distinct modules: one for "date/time" management (~wallclcok) , and one for "relative time" (realtime clock). Also rename the RealTime* API which is confusing regarding the CLOCK_REALTIME macro from linux kernel.

This rework must also rework the dependancy order, so that the platform-dependant specific file are not referenced by non-platform dependant files (anticipates #1108 (closed))

Edited Aug 22, 2024 by Jérémie Chabod

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