fix: escape hatch snapshots

[LHerskind]

In the implementation we had just a single value to store the escape hatch, but since it is updatable by governance, and are not always used with exactly the value that it currently has, we are back into the good ol' case of snapshots.

Essentially, when there is only one value for the escape hatch to look at, the consumers (which might depend on specific timing) could retroactively have their logic altered.

Consumers:

• Epoch Proof Library
• Invalidation Library
• Propose Library
• Slashing

By being able to alter "all" view of the escape hatch it was possible to make failure cases as these:

• After a hatch has been used to submit checkpoints, the escape hatch is updated, and when it comes time to prove, the proof will fail because no committee signatures 😭
• As above, possible to invalidate the block early
• If the update happens after a provider was selected but before their duty starts, they could end up in a case where it is impossible for them to propose and they will then get punished because they also did not prove anything
• For the case of slashing, because we do not slash during the escape hatch, it could be abused to avoid slashing entirely.

Another point of interest, not for the rollup, but for the candidates, is that the escape hatch could keep selecting them for duty, without being able to actually propose. So the escape hatch must also take a look at the rollup to see if it is currently the active hatch.

Solving the problems are as mentioned simple, use a snapshot, and then read historical values. When updating the escape hatch we will then do it for the NEXT epoch, since it could otherwise happen after a checkpoint was already proposed in the same L1 block.

In the case where the update happens during an open hatch, we allow the proposer to do nothing without getting punished, but if he does propose thing he must fulfill them.

[LHerskind]

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• fix: misc minor contract fixes #20423
• fix: escape hatch snapshots #20363 👈 (View in Graphite)
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• fix: skip empty epochs in tally slasher #20361
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