Remove audio engine isolation queue

[sbooth]

No documentation for AVAudioEngine that I can find states that the object may only be used from a single thread/queue. On the other hand, no documentation that I can find states that it is safe to use the object from multiple threads/queues either.

AVAudioEngine appears to use mutexen internally to protect graph modifications, so this PR removes the extra logic and overhead associated with the audio engine isolation dispatch queue.

[Copilot]

Pull Request Overview

This PR removes the audio engine isolation dispatch queue (mEngineQueue) that was previously used to serialize access to the AVAudioEngine instance. The change is based on the assumption that AVAudioEngine uses internal mutexes for thread safety.

Key Changes:

• Replaced the withEngine: callback-based API with a direct audioEngine readonly property for accessing the underlying AVAudioEngine
• Removed all dispatch_async_and_wait(mEngineQueue, ...) calls throughout the codebase, simplifying the code and reducing overhead
• Removed the SFBAudioPlayerAVAudioEngineBlock typedef that was used for the callback pattern

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 3 comments.

File	Description
Sources/CSFBAudioEngine/include/SFBAudioEngine/SFBAudioPlayer.h	Replaced withEngine: method with audioEngine property; removed block typedef; updated documentation
Sources/CSFBAudioEngine/Player/SFBAudioPlayer.mm	Updated implementation to return audioEngine property instead of executing callback
Sources/CSFBAudioEngine/Player/AudioPlayer.h	Removed mEngineQueue member variable; replaced WithEngine method with simple GetAudioEngine getter
Sources/CSFBAudioEngine/Player/AudioPlayer.mm	Removed queue creation in constructor; eliminated all dispatch queue synchronization in engine operations, volume control, device management, and logging

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