Some time ago, we agreed to let clang-format-18 format our C++ code.

By now, not all code is still formatted this way.

So, the next step in this endeavor:

• Re-format our code one more time.
• Add a check to our automated builds, so code that is not formatted in that way will be flagged at PR level.
• Add a stance to our CONTRIBUTING.md file that explains how to format contributions.