Verify Ed25519 support in PKCS#7

Currently, we support PKCS#7 signatures using Ed25519, however there are no public test vectors available to verify the correctness of the implementation. As such, we should verify the implementation once these become available, or disable Ed25519 support for PKCS#7 if they are not made available prior to release.

• https://tools.ietf.org/html/draft-ietf-curdle-cms-eddsa-signatures-06