Convert mentor notes to approaches

See [forum](https://forum.exercism.org/t/fix-syntax-in-space-age-mentoring-notes-on-python-track/19954/8) for context.

There are a bunch of mentoring notes on the [website-copy repo](https://github.com/exercism/website-copy/tree/main/tracks/julia/exercises), which were used in earlier versions of Exercism. Now (late 2025), many people have forgotten that these exist, which is a waste.

It would be better to have these as [Approaches](https://exercism.org/docs/building/tracks/approaches), so that mentors can easily access them, and they are available to students after completing the exercise.