Improve error handling for compile_project

[austinabell]

When passing an invalid path to the crate, there is simply the error:

Error: No such file or directory (os error 2)

Where it would speed up development a lot if it also included the file path it was trying to hit (devs might not know it's trying to search from the crate directory)

repro:

workspaces::compile_project("./some_non_existent").await.unwrap()