Tests for the infrastructure used for running consensus-related tests.

The library ouroboros-consensus-test provides a bunch of test utilities that we use throughout the consensus layer tests. Here we test this infrastructure. Some examples of aspects we test here include:

• Some consensus tests override the leader schedule from the underlying protocol, instead explicitly recording which nodes lead when. If we use a round-robin schedule for this, and then compute the expected fork length, we'd expect to get no forks at all.
• Some invariants of various utility functions.