feat(coreaudio): make Stream implement Send on CoreAudio

[roderickvd]

Stream can now be moved between threads safely on macOS.

• Replaced Rc<RefCell<>> with Arc<Mutex<>> for thread-safe access to stream state
• Extracted device disconnection handling into a separate DisconnectManager to isolate non-Send AudioObjectPropertyListener
• Removed unnecessary unsafe impl Send implementations that are now automatically derived

The mutex is only locked during play() and pause() operations, so performance impact is negligible. The audio callback is completely unaffected.

[dvdsk]

I suspect we can not do this without spawning a separate thread to keep AudioObjectPropertyListener in. Maybe its perfectly safe maybe its not. There is not enough documentation from Apple to judge that.

Lets give Apple users an extra thread doing nothing but keep that object on the same thread.... We should name the thread: apple_should_document_their_audio_api \s

[roderickvd]

@dvdsk good catch. Let's be more conservative. I've reworked this to use a dedicated thread.

While I was at it, I also killed the Clone impl on Stream. That's just confusing, and ALSA and WASAPI don't have it either. Should be much cleaner now.