Want test cases from C Tor for hs time period calculations

In !987 (merged) we implemented the HS time period calculations. These are super complicated and confusing.

C Tor has a set of test cases in src/test/test_hs_common.c in test_client_service_hsdir_set_sync and nearby. We should try to copy all these into Arti as test vectors, to make sure we do precisely the same thing as C Tor.