Whisk: assert zeroed values during selection gap

[dapplion]

Whisk requires to not submit tracker shuffling during a selection gap. To have more deterministic block production the spec should assert whisk_shuffle_proof_M_commitment and whisk_shuffle_proof to be zero. It should also assert whisk_post_shuffle_trackers to be zero instead of pre_shuffle_trackers. Setting the values to pre_shuffle_trackers does not add any new information while increasing the number of non-zero bytes in the block increasing its compressed size.

[asn-d6]

I think the idea we had with @JustinDrake here is that the proposer would create a valid shuffle proof but would use the identity permutation (i.e. not permute at all). We did this so that the consensus logic does not have a too complicated special-case during that selection gap.

If you think that the proposer should instead send nothing during selection gap, we should strongly consider it.

[dapplion]

I my PoC I have to already consider the selection gap in the block production logic. This change does not add any more complexity IMO

[asn-d6]

I my PoC I have to already consider the selection gap in the block production logic. This change does not add any more complexity IMO

Aight, makes sense. can you also update the obsolete comment regarding unchanged trackers, please?

[asn-d6]

LGTM! Thanks!