Update api to enable custom runtime

[pgherveou]

This PR update how the API is structured:

the Runtime trait is gone. The way it was structured,made it impossible to bring in an existing Runtime and pass it to a drink or ink! test. This PR moves these APIs to a SandboxConfig trait, and make the Sandbox generic over that trait.

This let us write tests like this

impl_sandbox_config!(
    struct MyConfig {
        runtime: MyRuntime;
        default_balance: DEFAULT_BALANCE;
        default_actor: ALICE;
    }
);

#[drink::test(config = MyConfig)]
fn test_flipping_with_custom_runtime(mut session: Session) -> Result<(), Box<dyn std::error::Error>> {
    // snip
}

this create_minimal_runtime macro is still there, it just now call the new impl_sandbox_config macro internally to implement the SandboxConfig trait.

I have an upcoming PR to ink! that will leverage these new API to call e2e tests against a custom runtime. Specifically it will be used with the pallet-contracts-mock-network crate to test XCM host functions

use pallet_contracts_mock_network::{parachain::Runtime as ParachainRuntime, ALICE};

impl_sandbox_config!(
    struct ParachainSandbox {
        runtime: ParachainRuntime;
        default_balance: 1_000_000_000_000_000;
        default_actor: ALICE;
    }
);

/// Positive case scenario:
#[ink_e2e::test(backend(runtime_only(runtime = ParachainSandbox)))]
async fn transfer_with_xcm_execute_works<Client: E2EBackend>(
    mut client: Client,
) -> E2EResult<()> {
    // snip
}

[pgherveou]

can you please elaborate on why the previous API was inconvenient? the difference is quite subtle

With the current API we expect that our (frame) runtime also implement drink::Runtime. We can do that because we create the runtime with the macro, so it's local to the crate where we use it.

If instead we try to bring in a (frame) Runtime that is declared in another crate. Then because of the orphan rule we won't be able to implement the foreign trait (drink::Runtime) on our (foreign frame) runtime.

To make this use case work, this change compose drink::Runtime inside a new Config trait, instead of using trait inheritance

[pgherveou]

For reference this is how I am using this PR in ink!

https://github.com/paritytech/ink/blob/b0762ce5c066d66ffb9f8b27ff58ae9a2e9a1974/crates/e2e/src/drink_client.rs#L463-L479

/// Exposes preset sandbox configurations to be used in tests.
pub mod preset {
    use drink::impl_sandbox_config;
    use pallet_contracts_mock_network::{
        parachain::Runtime as ParachainRuntime,
        ALICE, INITIAL_BALANCE
    };

    drink::impl_sandbox_config!(
        #[doc = "A Sandbox configuration for the parachain runtime of pallet-contracts-mock-network."]
        pub struct ParachainConfig {
            runtime: ParachainRuntime;
            default_balance: INITIAL_BALANCE;
            default_actor: ALICE;
        }
    );
}