This fixes a build failure on MacOS Sonoma when the copy plugin step
is enabled.

This allows real-time threads to join an audio workgroup on Apple platforms.

This fixes a warning when running xcodebuild directly

Enabling the hardened runtime also enables library validation, which
means that the manifest generator may not be able to load the built
plugin if the generator runs before the signing step.

The manifest generator tools should not be distributed/archived, so
disabling the hardened runtime for these targets is appropriate.

- added unit tests
- best performance timers used for each platform
- fixed an issue in which timer callbacks could drift

This reverts commit 82377a787a.

Reintegrates changes from cf9fc84669