Multi-call

[MujkicA]

Closes #211

This PR introduces the MultiContractCallHandler for bundling contract calls into a single transaction. It provides a similar interface to ContractCallHandler.

let call_handler_1 = contract_instance.initialize_counter(42);
let call_handler_2 = contract_instance.get_array([42; 2].to_vec());

let mut multi_call_handler = MultiContractCallHandler::new(wallet.clone());

multi_call_handler
    .add_call(call_handler_1)
    .add_call(call_handler_2);

let (counter, array): (u64, Vec<u64>) = multi_call_handler.call().await.unwrap().values;

Alternatively, the response can be fetched like this if we want to have access to receipts and logs in the MultiCallResponse:

let response = multi_call_handler.call::<(u64, Vec<u64>)>().await.unwrap();

The harness is extended with a test for the regular work flow and one for the script workflow (exposes script). Another test is added to script.rs for verifying that script data i built correctly.

[digorithm]

It may look simple, but this line took us days of debugging and redesign to get right 😂

[MujkicA]

Also the trick with bundling the output tokens of all the separate calls into a Token::Tupple so that the generic D effectively covers multiple types to avoid the need for dynamic dispatch

[adlerjohn]

nit

[segfault-magnet]

Whenever I see somebody do something smart I wonder 'would I have thought of that?'

Let's just say I've been doing a lot of wondering :D

Great work.

[digorithm]

LGTM -- great work!