regenerate lakefile

[oxe-i]

This change is mostly to update the lakefile.toml of all exercises to keep it in line with the online test runner. The online test runner treats warnings as errors, but this was not the default when students work locally.

I also updated the generator script so that -r (regenerate) now adds all files in the templates folder to every exercise in the exercises/practice folder. Before, it was only adding the toolchain. This means we now have an easy way to propagate any change that affects all exercises (Lean version, additional modules, changes in the testing library, etc.).