Function sign_delegation 

fn sign_delegation<CTX: ContextTr<Db: DatabaseExt>>(
    ccx: &mut CheatsCtxt<'_, CTX>,
    private_key: Uint<256, 4>,
    implementation: Address,
    nonce: Option<u64>,
    cross_chain: bool,
    attach: bool,
) -> Result<Vec<u8>>

Helper function to sign and attach (if needed) an EIP-7702 delegation. Uses the provided nonce, otherwise retrieves and increments the nonce of the EOA.