[cm/pub/] with Classic McEliece 6960-119 + X25519.
=> https://classic.mceliece.org/ Classic McEliece
=> https://datatracker.ietf.org/doc/html/rfc7748.html X25519

Combined Classic McEliece 6960-119 and X25519 public keys are used
for KEM purposes, so should have "kem" key usage set.

Its algorithm identifier is "mceliece6960119-x25519".
Its public key value is a concatenation of 1047319-byte
mceliece6960119 public key and 32-byte X25519 one.

Public key's fingerprint should be calculated using SHAKE128.
=> https://keccak.team/ SHAKE XOF function

Optional "/data/prehash" field can contain the SHAKE256 hash
of the concatenated public keys in "/data/pub/0", that could
save resources during [cm/kem/mceliece6960119-x25519-hkdf-shake256]
KDF calculations.
