Function generate_keypair 

pub fn generate_keypair(
    alg: Algorithm,
) -> Result<(Vec<u8>, Zeroizing<Vec<u8>>), AlgorithmError>

Generate a raw keypair for the given algorithm.

This is supported for:

• signature algorithms
• key agreement algorithms
• KEM algorithms

Returns (public_key, secret_key); the secret half zeroizes on drop.