[FIX] UniqueIdGenerator susceptible to identical RNG seeds

The bug appeared when running a TOPPAS pipeline where GenericWrappers %%RNG macro was used (which uses UniqueIdGenerator internally). Two output files got assigned the same name since their GenericWrapper instance was started within a 1 second interval -- leading to overwriting of files...

fixed time resolution of seed initialization: was seconds, now microseconds (hard to do better, and should be sufficient)