Improve hydration behavior and flag name

[fa-sharp]

The changes in #42 are working pretty well. The only thing I've noticed is that when I change the value of key, there is a brief moment where the app is still rendering the old value, before loading the value of the new key. This can cause unintended flashes of old content. Ideally, the render value should reset to onInit (or run onInit if it's a function) during that brief period, until the new key is hydrated.

The solution is pretty simple - we just need to reset the render value to onInit in the cleanup function here:

storage/src/hook.ts

Lines 92 to 95 in 282b946

	return () => {
	isMounted.current = false
	storageRef.current.unwatch(watchConfig)
	}

Another related (small) issue - there is a useful boolean flag in the onInit function to determine the hydration status. I think isHydrated would be a better name than isHydrating for what it's indicating. It is set to true when the value has been actually loaded from storage:

storage/src/hook.ts

Line 10 in 282b946

type Setter<T> = ((v?: T, isHydrating?: boolean) => T) | T

I can submit a PR when I have a chance :)