make state fingerprint available

[damip]

• document all added functions
• try in sandbox /simulation/labnet
• unit tests on the added/changed features
  • make tests compile
  • make tests pass
• add logs allowing easy debugging in case the changes caused problems
• if the API has changed, update the API specification

[Leo-Besancon]

The code looks pretty straightforward to me. However, we have to be careful about timings. Because we do not have a "final_state_hash" field on the final_state, two nodes may show a different fingerprint if atomicity is not verified during a slot.
I think it should not cause a problem in most cases, but it could.

For example: we edit the final_state_hash_snapshot of a cycle after finalizing a slot, which changes the hash.

We could solve this by restoring a final_state_hash field that syncs with the db hash while finalizing, or by querying the last available final_state_hash_snapshot in cycle history, or some other way I have not think about :)

[damip]

@Leo-Besancon writes to the final state happen only under an execution write lock. And query_state read-locks it. So it should be ok. Do you confirm ?

[Leo-Besancon]

@Leo-Besancon writes to the final state happen only under an execution write lock. And query_state read-locks it. So it should be ok. Do you confirm ?

Yes it makes sence, as the versioning batches are also written on finalization now. Maybe we should add a comment in the fingerprint function that this is the expected behaviour for it to work (only one write, with a lock, per slot).