Add External Favicon Preloading Logic

[princefishthrower]

Within the usePleaseStay source code there is a TODO to add preload logic for external favicons. You may notice when opting to take external favicons, the favicons sometimes take a moment to appear when being swapped, as they are loaded directly from the URL, and not a local asset.

To fix this, the following should be possible:

• On hook mount, for each external favicon provided, the favicon should be 'downloaded' and stored somehow
  • perhaps in LocalStorage
  • perhaps in a cookie
  • perhaps even appended and hidden into the DOM somewhere - though this wouldn't work as well for static sites with multiple pages)
  • note this requires determining in the first place if the favicon is external - a regex may do nicely here

I'm open to any options, as long as it gets the job done and is not overly complex!