Add Concept Exercise: `magical-measurements`

[0xNeshi]

Towards #103

Scaffold https://github.com/exercism/cairo/blob/main/exercises/concept/magical-measurements

Instructions for the exercise are already given (see .docs/instructions.md). Follow the instructions yourself to implement all the other necessary (missing) files/tests/content.

TODO:

• use other implemented concept exercise metadata files for inspiration, e.g. https://github.com/exercism/cairo/tree/main/exercises/concept/lucians-luscious-lasagna
  • instructions.md are already given
  • implement introduction.md
  • implement design.md
  • implement hints.md
• implement the example solution in .meta/exemplar.cairo
• implement the exercise stub at src/lib.cairo
• implement tests for the exercise at tests/magical_measuremets.cairo
• replace <your_gh_username> placeholder with your actual GH username in .meta/config.json