cbor serialization of big integers (Uint) is undefined

I really thought we had this written down at some point as using a cbor big int, but i can't seem to find it.

In any case, We should use cbor big ints here (its an extension). It costs us one extra byte for the tag, but means other CBOR parsers can more easily understand our datastructures.

Start with issue #445 and locate the specification text defining CBOR serialization for Uint values. Compare the current rule with the CBOR big-integer extension and determine where the requirement belongs. Done means the specification clearly states the encoding and its compatibility implications.

Written by the indexing model from the issue text.