feat: ChonkyBFT logic

[brunoffranca]

• Everything in chonky_bft folder is basically new.
• UTHarness was moved to chonky_bft/testonly.rs. Several changes to it though.
• All tests that use UTHarness were moved to chonky_bft/tests. Some of the old unit tests were repurposed, but a fair amount of the tests in chonky_bft/tests are new.
• The tests in tests.rs were split between tests/mod.rs and tests/twins.rs (except for a few that used UTHarness and were moved as said before). There were no changes to them though.

Part of BFT-452

[brunoffranca]

One thing I wanted to note is that I don't actually check anywhere that reproposals don't have a payload set. This technically is not necessary since the consensus just ignores the payload. But maybe we want to do that check anyway.

[pompon0]

Yes, for defence in depth, please check that payload is included if and only if it is required.