[cm/pub/] with Ed25519-BLAKE2b.

Same calculation and serialisation rules must be used as with
[cm/signed/ed25519-blake2b].

Public key's fingerprint should be calculated using BLAKE2b hash
with 256 bit output length specified.

Algorithm identifier for the public key: "ed25519-blake2b".

=> https://cr.yp.to/ecdh.html X2559, key-agreement algorithm
=> https://datatracker.ietf.org/doc/html/rfc7748.html RFC 7748, same
=> https://www.blake2.net/ BLAKE2b hashing algorithm
=> https://datatracker.ietf.org/doc/html/rfc7693.html RFC 7693, same