static Kem dHKemX25519HkdfSha256() {
        return new DHKemX25519HkdfSha256(KeyUtils::generateX25519KeyPair);
    }
@return a <code>HKEM(X25519, HKDF-SHA256)</code> instance that generates new ephemeral X25519
        key pairs from a secure random source per {@link #encap(XECPublicKey)} invocation.
security-utils/src/main/java/com/yahoo/security/hpke/Kem.java