Implement `Issuer` interface for `type1`, `type2`, and `typeF91A`

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](https://github.com/smhendrickson/draft-hendrickson-pp-attesterissuer) draft.