Implement Issuer interface for type1, type2, and typeF91A #48
Description
Arbitrary batched tokens introduce an Issuer interface. This interface could be move below github.com/cloudflare/pat-go/tokens if it was implemented by all token type.
It was not implemented in #46 because not directly connected, but would help to simplify future use of arbitrary batched tokens.
This is also work that should be done with attester-issuer draft.