Make TestingTorNetwork produce consensuses quicker

First, trim time intervals as much as possible while keeping everything stable. The current 5 minutes between voting could perhaps change to 2. We might need to adjust other timings -- exhcanging votes and signatures. Also, we might need to revisit the directory refetch schedule which is changing in #6752 (moved).

Second, let's add an option to Tor in which we can pass an offset, in seconds, to generate a consensus following a custom schedule every 5 minutes (or whatever we might change that to), rather than having to wait for the next 5-minute interval. Example: Offset 75s would mean that the consensus would be from 00:01:15 rather than 00:00:00.