docs: comments are now more specific in code style.

[Jaskowicz1]

This PR makes comments more specific in the code style, as it now has a demonstration of how we want comments, along with defining how general comments in a cpp should look (as we've have several cases of a mis-match in comment styles).

This PR also moves all the code from the coding style guide, into its own folder in example_code. This code isn't checked by the examples runner so it won't ever cause issues.

Documentation change checklist

• My documentation changes follow the same style as the rest of the documentation and any examples follow the coding style guide.
• I tested that my change works before raising the PR (via running doxygen, and testing examples).
• I have not moved any existing pages or changed any existing URLs without strong justification as to why.
• I have not generated content using AI or a desktop utility such as grammarly.

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