WIP: Multi Root Contexts

The design/approach/API is ready for critique, all tests pass. Edit: now that I think about it, I should probably explain the changes. A lot of stuff had to be done to prevent circular dependencies. But I'll have to do that later. Warning: - Linting/formatting is a complete mess - I need to add more type info and break out some minor changes (like the flake.nix) into a separate PR. I just wanted to get this out so you could take a look in the meantime (might be several weeks/months before I get enough free time to check back in on this)