cargo and rustc need work:

- sccache helps with some parts of builds but rustc needs to be caching a whole lot more for rapid TDD iterations. It shouldn't take seconds or many minutes to build things. (Invoke "go does it in milliseconds" card.)

- cargo should migrate away from git and sparse protocols. Both are slow because one abuses git and the other fetches each crate metadata as a file using individual requests. It would be faster and simpler to send either a total compressed sqlite database OR a compressed SQL transaction to migrate between versions. N files on disk representing each crate is asking for fs performance problems in the real world on fses people actual use.