Scoru,Proto: introduce versioned commitments

Context

Part of #2906 (closed)

To prepare migration of smart-contract rollup, we should add a version number to all values in the storage.

With this merge request, we will be able to introduce a V2 commitment in the storage. That is, when a value of type versioned is read from the storage, it is transformed to t which is the latest commitment version. The potentially most critical code in this merge request can be of_versioned because the actual migration would happen here, but as there is for now no migration, I believe the code is safe.

Given the actual set-up of a unique version, the drawback of this MR is a bit of boiler-plate code and an additional byte in the binary representation.

Manually testing the MR

TODO: Does it needs additional tests? I guess that until we have a real migration transforming a V1 commitment to a V2 it doesn't need much tests?

Checklist

• Document the interface of any function added or modified (see the coding guidelines)
• Document any change to the user interface, including configuration parameters (see node configuration)
• Provide automatic testing (see the testing guide).
• For new features and bug fixes, add an item in the appropriate changelog (docs/protocols/alpha.rst for the protocol and the environment, CHANGES.rst at the root of the repository for everything else).
• Select suitable reviewers using the Reviewers field below.
• Select as Assignee the next person who should take action on that MR