Function setup_network 

pub async fn setup_network<'a, N: Netstack>(
    sandbox: &'a TestSandbox,
    name: &'a str,
    metric: Option<u32>,
) -> Result<(TestNetwork<'a>, TestRealm<'a>, TestInterface<'a>, TestFakeEndpoint<'a>)>

Sets up a realm with a network with no required services.