AS | Use hex encoding rather than base64 in parsed claims

[Xynnn007]

We are using hex in [tdx claims](https://github.com/confidential-containers/trustee/blob/main/attestation-service/verifier/src/tdx/claims.rs#L67, sgx claims, azure vTPM claims. Also base64 in SNP.

I suggest that we should use a common encoding, which would make the policy writing work easier.

[larrydewey]

I agree, we should unify on a single encoding practice. If I remember correctly, I believe base64 was selected because of how the qemu interfaces were defined, though I could be remembering incorrectly. @fitzthum do you happen to know off the top of your head?