split distribute_time into two methods for better time handling

[maurerle]

This makes it easier to handle distributed clocks.

Before, we had to distribute the time twice to ensure, that to round trips took place (send, wait, ask for time). This is now clearer in the code by splitting the time distribution and the waiting task into two separate messages of the distributed clock manager. See also this comment: https://github.com/OFFIS-DAI/mango/pull/82#issuecomment-2276253330

• add test for both of these handlings
• make sure that agents sleep correctly until messages are retrieved by agents
• this gives a central partially ordered clock (which still allows concurrency)

[maurerle]

Thanks for your review, do you have time to look again? :)