Formalize and implement versioning of stake authorization messages

[aesedepece]

Wit/2.1 is expected to introduce new fields in stake authorization messages, such as delegation expiration and take rate. To ensure backward compatibility and smooth network upgrades going forward, we need to formalize and implement a versioning mechanism for stake authorization messages.

This will allow:

• Future-proofing the format of stake authorization messages
• Supporting nodes and tooling to distinguish between message versions
• Enabling new features in delegation (e.g. expiration, validator commission) without breaking existing functionality

[aesedepece]

I'm currently assessing whether "this authorization can only be used by a stake transaction before this timestamp" field is necessary in the authorization message; to avoid stakers abusing old authorizations signed under terms that are no longer reasonable.

Alternatively, instead of a "not after" timestamp, we could just add the current timestamp into the authorization message and simply establish that authorization messages expire after 24h.