rustpkg: Build files into .rustpkg without unique names and then install them into ~/.rustpkg with unique names #4962
Description
See the end of #4610 for more information. NB. Rustpkg hasn't landed yet, but it's been approved. Kind of also need a command like rustpkg run <crate> that runs a crate (compiling it if it hasn't been) in .rustpkg, for running binaries without installing them (and not asking the user to run it from in .rustpkg..).