Apply clock changes to running nodes in the consensus tests

[edsko]

As part of IntersectMBO/ouroboros-network#759 (PR IntersectMBO/ouroboros-network#1554) we introduced tests for the BlockchainTime in the presence of an unstable clock. However, it would be good to extend also the consensus tests to apply clock changes, to catch stuff like IntersectMBO/ouroboros-network#1570 and IntersectMBO/ouroboros-network#1544 (comment) .

[nfrisby]

Thomas and I think that Issue #753 is essentially blocking this: letting the nodes' clocks jump independently will effectively introduce clock skew.

Letting the nodes' clocks all jump together, remaining in sync, seems less interesting, but it would almost certainly be easier to test.

[edsko]

Unless UTCTime is reset, that doesn't seem particularly useful to test 😁