tvix-cli: split out store/eval glue code

We should split out all the glue code for store and eval into its own crate, and have the CLI only do the CLI parsing.

• The error struct is not public
• It's not possible to access derivation or known_paths

This makes it hard to write test benches, or things using the derivation builtin.

It might make sense to think about the ergonomics for how to create a tvix evaluator that's able to evaluate nixpkgs. Related to b/262 too.

1. flokli updated the body of this issue at 2023-10-19T11·45+00
2. flokli updated the body of this issue at 2023-10-19T11·47+00

3. cl/9908, cl/9909, cl/9910.

   flokli at 2023-11-03T12·11+00

4. This has been done, can be closed.

   flokli at 2023-11-15T22·10+00

5. flokli closed this issue at 2023-11-15T22·10+00