fix: Better test for exercises/10_modules/modules1.rs

[JiwaniZakir]

Fixes #2339

The modules1 exercise could be passed by commenting out the call in main, since no test enforced that make_sausage() must be public. Adds a #[cfg(test)] block to exercises/10_modules/modules1.rs that calls sausage_factory::make_sausage() directly, and sets test = true in rustlings-macros/info.toml so rustlings actually runs cargo test against the exercise.

[JiwaniZakir]

Closing this PR as it hasn't received maintainer review. Happy to resubmit if there's interest.

[senekor]

I'm not sure what this would improve. The new tests can also just be commented out. We don't need to prevent cheating, since we assume users do these exercises voluntarily.

We could possibly add a comment above the main function, telling users not to change it, in case it's unclear. But that seems pretty obvious to me from the context.