Function sign_bytecode 

pub fn sign_bytecode(
    bytecode: &[u8],
    private_key: &[u8; 32],
    timestamp: Option<u32>,
) -> Signature

Sign bytecode with an Ed25519 private key.

private_key must be exactly 32 bytes (seed material for ed25519-dalek). The signature covers the SHA-256 fingerprint of the bytecode concatenated with a 4-byte little-endian timestamp.