dart-flute-todomvc-wasm creates a new instance on each iteration #180

It seems like this is somewhat intentional.

    // Instantiate each iteration, since we can only `invokeMain()` with a
    // freshly instantiated module.
    const additionalImports = {};
    const instantiatedApp = await this.compiledApp.instantiate(additionalImports);

I'm a little unsure if this is something we want to measure on each iteration however. It seems like each iteration of this benchmark is meant to represent some UI update. I don't think most Dart pages would instantiate a new instance for that. Should we try to restructure the code to not instantiate on each iteration?