Rust run in separate file breaks

When using `Script:run` with a active file that is not `main.rs`, it returns an error that a main function cannot be found.

This boils down to script probably trying to run the current file, than running the project's main file.

With some guidance, I can provide a PR to help fix this/add the behavior since its a little annoying. Alternatively, can script options be used to achieve the same goal?