Separate types from plans

[cefn]

This simplifies the original noredux-async application, isolating just the plan part, and putting the typescript type declarations elsewhere so the complexity of the plans.ts file is more comparable with e.g.

• Redux equivalent app https://codesandbox.io/s/github/reduxjs/redux/tree/master/examples/async?file=/src/reducers/index.js
• XState equivalent app https://codesandbox.io/s/xstate-react-reddit-example-with-actors-5g9nu?from-embed=&file=/src/subredditMachine.js