Yellow squiggly lines begone!
Done automatically on .cpp files through `run-clang-tidy`, with manual corrections to the mistakes.
If an import is directly used, but is technically unnecessary since it's recursively imported by something else, it is *not* removed.
The tool doesn't touch .h files, so I did some of them by hand while fixing errors due to old recursive imports.
Not everything is removed, but the cleanup should be substantial enough.
Because this done on Linux, code that isn't used on it is mostly untouched.
(Hopefully no open PR is depending on these imports...)

Co-authored-by: OatmealDome <julian@oatmealdome.me>

Common: Replace enable_if with concepts and other minor modernizations.

Config: Add locking for config changed callbacks

Update clang-format to version 19

Different threads are adding and calling callbacks, so this should have
some locking. This is both to ensure thread safety when accessing
`s_callbacks` and to ensure that there won't be situations where a
callback gets called after it's removed.

`s_callback_guards` is also accessed from multiple threads and has
therefore been made atomic.