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.

Require callers of Config::AddConfigChangedCallback and
CPUThreadConfigCallback::AddConfigChangedCallback to handle the returned
ConfigChangedCallbackIDs to hopefully prevent future issues with
callbacks getting called after their associated objects have been
destroyed.