proof of concept for async data fetching from Python -> JS

[kylebarron]

deck.gl TileLayer where each getTileData requests data from Python as necessary.

We should have from_rasterio and from_async_tiff (or maybe some other API that shows that async_tiff is preferred?).

Then each constructor should create a TMS document representing the input. Then we should send that TMS to the frontend for it to know how to fetch data from Python.

Note that if we just have a generic tms rendering layer, then we don't need a hard distinction between COG and Zarr.