feat: introduce pre-commit framework

[ahans]

To avoid confusion, I updated this PR now to only use pre-commit to replace (and fix) the
existing clang-format checks. Other checks can be added in follow-up PRs.

Here is the commit message from the commit that does the actual switch. The other commit reformats all the files that went through without proper formatting due to the bug in the setup:

---

This replaces the custom clang-format script with the pre-commit framework,
making it easier to add checks in the future and simplifying GitHub
integration.

The GH workflow is adapted to run checks now as well.

To use it locally, all you need to do is install pre-commit locally, typically
via:

pip3 install --user pre-commit

You can then run pre-commit run --all to run it locally. Note that this does not install
a Git hook. If you want that as well, run pre-commit install.

For more details on pre-commit and other installation options, see
https://pre-commit.com/ and https://pre-commit.com/#install

[github-actions]

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[github-actions]

This PR touches files which potentially affect the outcome of the tests of an exercise. This will cause all students' solutions to affected exercises to be re-tested.

If this PR does not affect the result of the test (or, for example, adds an edge case that is not worth rerunning all tests for), please add the following to the merge-commit message which will stops student's tests from re-running. Please copy-paste to avoid typos.

[no important files changed]

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[vaeng]

I did not check every single file, but it seems to work on the ones I tried.

[vaeng]

Is this file needed for the PR?

[ahans]

Probably not. I opened this accidentally against this repo instead of my fork. It's not cleaned up in any way yet. Just wanted to showcase how it could look like. I can clean up this PR and let you know when I'm done. Then you can do a proper review.

[ahans]

That file had some whitespace violation. I removed those checks now from this PR. This now is strictly only clang-format.

[ahans]

I ran all practice exercises through the test runner to find the ones that needed manual formatting, because clang-format would split long test names over multiple lines. All occurrences are fixed now.

[vaeng]

I ran all practice exercises through the test runner to find the ones that needed manual formatting, because clang-format would split long test names over multiple lines. All occurrences are fixed now.

That would have been my final question. Thanks for all the work on this one.

[vaeng]

I merged your other PR. Can you please fix the conflicts, so we can merge this and have beautiful formatting?

[ahans]

I merged your other PR. Can you please fix the conflicts, so we can merge this and have beautiful formatting?

Ok, just saw your approval and comment here. We could have just closed the other PR without merging if we're going with this version. Using both works as well, of course.

[ahans]

Alright, it's rebased now. However, there was one other potential "issue" I wanted to point out. The solution templates that only have the namespace, e.g.,

namespace diamond {

}  // namespace diamond

with the current clang-format config get reformatted to look like this:

namespace diamond {}  // namespace diamond

I find this non-ideal, since a student would have to navigate inside {} and hit return there.

We could fix this with a comment:

namespace diamond {
    // TODO: implement solution
}  // namespace diamond

Then the student would still have to remove the comment, but still better than having {} IMHO.

Alternatively, we could use the clang-format option KeepEmptyLinesAtTheStartOfBlocks. I haven't tested this yet, but I think it would leave the template alone, since a namespace counts as a block in that context and the empty line would be at the beginning of the block. On the other hand, it would also leave empty lines in other places that we may not want. So I'm a bit torn on what to do.

Let me know what you think please!

[vaeng]

We could fix this with a comment:

I like this solution.
What do you think @siebenschlaefer ?