Add a Powerful Test VM

[rauljordan]

Description

This PR introduces a powerful test VM that implements the Host trait for the Stylus SDK. It supports mocking every hostio, and allows for mocking of calls, deployments, and checking log emissions. Moreover, it supports Foundry-style storage forking with a simple builder API:

let test_vm = TestVMBuilder::new()
            .contract_address(address!("2460d3db27c4bef88557e8dc9136e6fad189e8c3"))
            .rpc_url("https://sepolia-rollup.arbitrum.io/rpc") // Storage loads will fetch state from the RPC endpoint.
            .build()?

Calls can also be mocked:

#[test]
fn test_mock_calls() {
    let vm = TestVM::new();
    let target = Address::from([2u8; 20]);
    let data = vec![1, 2, 3, 4];
    let expected_return = vec![5, 6, 7, 8];

    // Mock a regular call.
    vm.mock_call(target, data.clone(), Ok(expected_return.clone()));

    let ctx = stylus_core::calls::context::Call::new();
    let result = vm.call(&ctx, target, &data).unwrap();
    assert_eq!(result, expected_return);

    // Mock an error case.
    let error_data = vec![9, 9, 9];
    vm.mock_call(target, data.clone(), Err(error_data.clone()));

    match vm.call(&ctx, target, &data) {
        Err(Error::Revert(returned_data)) => assert_eq!(returned_data, error_data),
        _ => panic!("Expected revert error"),
    }
}

Log emissions can also be inspected:

#[test]
fn test_logs() {
    let vm = TestVM::new();
    let topic1 = B256::from([1u8; 32]);
    let topic2 = B256::from([2u8; 32]);
    let data = vec![3, 4, 5];

    vm.raw_log(&[topic1, topic2], &data).unwrap();

    let logs = vm.get_emitted_logs();
    assert_eq!(logs.len(), 1);
    assert_eq!(logs[0].0, vec![topic1, topic2]);
    assert_eq!(logs[0].1, data);
}