payload property serves two purposes

[TimoGlastra]

The payload property serves two purposes: One is the unsigned/pretty payload that is used before the SD-JWT is signed, and then it is overwritten once the payload is signed with the correct _sd values etc..

This makes the value very vague, and incosistent, and I think it should be split up into two different properties, or at least one of the two purposes should not use the payload property if this value is exposed publicly.