[cm/pub/] with SNTRUP4591761+X25519.

Combined Streamlined NTRU Prime 4591^761 and X25519 public keys are
used for KEM purposes, so should have "kem" key usage set.

Its algorithm identifier is "sntrup4591761-x25519". Its public
key value is a concatenation of 1218-byte SNTRUP4591761 public key
and 32-byte X25519 one.

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

=> https://cr.yp.to/ecdh.html X2559, key-agreement algorithm
=> https://datatracker.ietf.org/doc/html/rfc7748.html RFC 7748, same
=> https://ntruprime.cr.yp.to/ Streamlined NTRU Prime KEM algorithm