This returns keys and a block forest created from them
This produces a block with an invalid id (and therefore signature)
given a valid block
This produces the genesis block
Offers the genesis block.
This strategy is a swiss-army tool to produce a low-level block
dependent on signer, round, parent and ancestor_id.
Note that the quorum certificate carried by this block is still placeholder: one will have
to generate it later on when adding to the tree.
This produces a round that is often higher than the parent, but not
too high
This produces an unmoored block, with arbitrary parent & QC ancestor