Check in CI that the build doesn't generate warnings

[sonmarcho]

It can happen that the compilation generates warnings (for instance, clippy warnings): I want to make sure it doesn't happen (i.e., all warnings are addressed before we merge).

[Nadrieril]

Could you elaborate?

[Nadrieril]

That's already the case today for the rust side: we pass -D warnings to cargo when building.

[Nadrieril]

And for the ml side also. I just checked both.