implement optional stale-while-revalidate behavior

[clockelliptic]

To Do: implement optional stale-while-revalidate behavior

Why:

• support & maximize progressive behavior
• allow stale or placeholder data to be shown optimistically while new data is loaded in the background, ideally in a non-blocking fashion

Acceptance Criteria:

• IDBSideloader constructor accepts an optional prop to enable stale-while-revalidate (swr) behavior
• swr behavior attempt to load cached data, and then re-fetches data in the background
• swr option is compatible with web worker option

example: IDBSideloader constructor prop

const loader = new IDBSideloader({ swr: true });

example: per-asset basis

<!-- attempts to show cached image data while re-validating/re-fetching -->
<img
  data-swr="true"
  data-src="user-statistics-chart.webp"
/>

Optional:

• implement similar API's & behaviors: https://swr.vercel.app/docs/api

see: https://www.mnot.net/blog/2007/12/12/stale