Add support for testing contract calls

[JulianGCalderon]

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snforge

Requested Feature

We should add support for tests like the following:

// This example was generated automatically by snforge.

#[test]
fn test_increase_balance() {
    let contract_address = deploy_contract("HelloStarknet");

    let dispatcher = IHelloStarknetDispatcher { contract_address };

    let balance_before = dispatcher.get_balance();
    assert(balance_before == 0, 'Invalid balance');

    dispatcher.increase_balance(42);

    let balance_after = dispatcher.get_balance();
    assert(balance_after == 42, 'Invalid balance');
}

Right know, calling this test fails because some cheatcodes are not implemented.

[FAIL] hello_starknet_integrationtest::test_contract::test_increase_balance

Failure data:
    "invalid selector: declare"

Solving this issue implies modifying some cheatcodes (declare/deploy), as well as the call_contract syscall.