Add coreaudio_direct module using coreaudio-rs safe wrappers for: - Device capability probing (supported sample rates, transport type) - Automatic sample rate switching per-track - Device lookup by name for CoreAudio↔CPAL bridging Uses a fork branch of coreaudio-rs that adds get_available_sample_rates and get_device_transport_type helpers (PR RustAudio/coreaudio-rs#149).