Function build_session_signing_bytes 

pub fn build_session_signing_bytes(
    nonce: u64,
    chain_id: u64,
    session_address: &[u8; 32],
    contract_ids: &[[u8; 32]],
    expiry: u64,
) -> Vec<u8> 

Build the signing bytes for set_session (Section 4.6 Step 3).

Layout: u64(nonce) + u64(chain_id) + u64(len(“set_session”)) + “set_session”

• u64(1) Option::Some + u64(0) [Identity Address discriminant] + session_address(32)
• u64(expiry) + u64(len(contract_ids)) + contract_ids(32 each)