fn generate_x25519_key_pair() -> Result<(HpkePublicKey, HpkePrivateKey), Error>Expand description
Generate a X25519 key pair expressed as a raw big-endian fixed-length integer.
We must disambiguate the AsBigEndian trait in-use and this function uses
AsBigEndian<Curve25519SeedBin>, which only supports agreement::X25519.
For generating P-256, P-384 and P-512 keys see generate_p_curve_key_pair.