New examples added!

Here's an update for y'all:

1. Instead of using the default Cesium Ion token, you now need to add your own in an .env.local or .env file (thus your Vercel/Next.JS deployment)
2. A user has emailed me about a Cesium Sandcastle demo not working properly (https://sandcastle.cesium.com/?src=3D%20Tiles%20Feature%20Styling.html) and I added an example on how to integrate this. In NextJS 13.4+ React strct mode is turned on by default; the consequence of this is that adding new layers without cleanup will add it twice only in dev mode this can result in really wonky results. You can either turn off strict mode, or add in a cleanup capability. The example now includes a cleanup example!
3. Some housekeeping.