Feature/async modifyup

[dxinteractive]

Addresses #280

dataparcels

• Amend: Some changes to translate's API
• Add: modifyUp() can now return an effect that can be used to trigger one or more async changes in response to a change. They are called after the initial triggering change has taken place, similar to how React's useEffect is called after render. They can produce any number of changes by calling the update function, which works just like parcel.update(). This makes them compatible with callbacks, promises and observables.

This will allow for heaps of code reduction in the library, as all internal async await based code can be re-written to use this instead.

Example of some async validation being written to some meta data.

parcel.modifyUp(({value}) => ({
    meta: {
        message: "Validating, please wait"
    },
    effect: async (update) => {
        let isValid = await validationRequest(value);
        update(() => ({
            meta: {
                message: isValid ? "Valid" : "Not valid"
            }
        }));
    }    
}));

[allanhortle]

What's up with this set timeout? seems like a magic number.

[dxinteractive]

It is yeah, but its essentially a throttle / debounce. It's quite like how React has a small delay / buffer to allow very fast subsequent changes to state to be treated as the same state update. I need to bucket all effect calls together to be able to dedupe them, as the thing that calls the effect function can be called multiple times as a change goes up through all the parcels. But I also have no way of knowing when the change is complete and I can stop buffering, because the parcels are all a bit decentralised, there is no god parcel that can say when a round of buffering should stop.