Consider having actual nested-seeds

[jkomoros]

Currently the whole library assumes that seeds are a single layer of depth and call out to other seeds with references. There's a lot of processing that goes on to take a possibly nested input and unroll it, and things like private, and manual manipulation in a diagram (#19) and fretting about the edge cases of "what if this private seed is called by another context"?

What if instead seeds were fundamentally able to be nested, and that was just always true?

We'd get rid of all of the duplicative machinery of nested vs unnested seeds, and be able to rip out a lot of unrolling machinery.

For the purposes of caching results, we'd use dotted name syntax to store intermediate products in the cases where you need to show intermediate results.

This would have implications throughout the stack but might end up being easier overall.