Use OSAllocatedUnfairLock instead of os_unfair_lock_ on supported platforms

[mluisbrown]

Fixes #854

For now macOS builds will still use os_unfair_lock_ until macOS 13 Ventura is released at which point this will need to be changed. It appears that you cannot refer to unreleased OS versions in @available and if #available statements 😞

NOTE:

CI is running Xcode 13.2.1 so tests will not test using OSAllocatedUnfairLock. CI should probably be updated to use Xcode 14.x. However, I ran tests locally with Xcode 14.0.1 and they passed. Looks like GitHub Actions will default to using Xcode 14.0.1 in the next few hours: actions/runner-images#6225

Checklist

• Updated CHANGELOG.md.

[mluisbrown]

Not sure why macCatalyst CI job is not working. It doesn't even start up 🤷

[NachoSoto]

This looks great, thanks!

[mluisbrown]

The macCatalyst job starts, but just seems to stall here:

That's the last output from xcodebuild that appears. It runs fine on my local machine.