There's no way to install packages/libraries to runner layer when using Rust provider

[PaulOlteanu]

aptPkgs/nixPkgs doesn't seem to apply to the [start] section in nixpacks.toml, and if a package is installed in a previous phase, it doesn't get copied over due to the use of onlyIncludeFiles.

I'm not even sure how this could work for multi-stage dockerfiles such as the rust one, but the size benefits for the final image are quite nice.

[plutack]

Same issue for go deploys too