MVP support for large (tiled) FITS images

[pkgw]

One of WWT's unique capabilities is its ability to work with very large images. But right now, pywwt can only expose FITS images that are less than 2048×2048 in size (I think it is), because images bigger than that need to be processed into tile pyramids to be rendered efficiently.

In order to give researchers access to this unique capability, we should start pywwt on the path towards supporting large tiled FITS images. Fortunately, I have been working on revitalizing the toasty library, which provides the base layer of code needed to create tile pyramids in Python.

We should investigate a Minimum Viable Product (MVP) version of automatic toasting of large FITS images in pywwt. There are a lot of open questions about how best to approach this, but we should start with something that delivers a reasonable UX and doesn't require too much extra engineering.