Function broadcast_key 

fn broadcast_key<CTX: ContextTr<Journal: JournalExt, Db: DatabaseExt>>(
    ccx: &mut CheatsCtxt<'_, CTX>,
    private_key: &U256,
    single_call: bool,
) -> Result

Sets up broadcasting from a script with the sender derived from private_key. Adds this private key to state’s wallets vector to later be used for signing if broadcast is successful.