Function crypto_sign_ed25519_sk_to_pk 

pub fn crypto_sign_ed25519_sk_to_pk(
    public_key: &mut PublicKey,
    secret_key: &SecretKey,
)

Extracts the Ed25519 public key from secret_key, placing the result into public_key.

Compatible with libsodium’s crypto_sign_ed25519_sk_to_pk.