Addressing VC-JWT "optionality and information loss"

We know that following v1.1 rules means loosing leap seconds when "instead of" path is taken.

We know that following v1.1 rules means loosing all `issuer` claims when "instead of" path is taken.

The proposal is to use "in addition to" for this test suite, and demonstrate that unix timestamps can be used without loosing any information.

And note that in the future, we might define a more specific mapping between `credential` and `verifiable credential` (in JWT format).

The action item is to ensure that both spruce and transmute can produce VCs that have complex issuer nodes in them the same way, and that `iss` is `issuer.id` or `issuer`.... and that other claims are preserved in the `jwt.payload.vc` attribute.