MilesAudio: Protect access to playing audio lists with a mutex

[seer-by-sentry]

Fixes CLIENT-RH. The issue was that: Miles Audio System callback thread accesses a freed AudioEventRTS object during file localization lookup, causing a Use-After-Free crash in std::_Hash due to lack of synchronization with the main thread's audio cleanup loop.

• Added a mutex to protect access to the m_playingSounds, m_playing3DSounds, and m_playingStreams lists.
• The Miles Audio callback thread and the main game thread can concurrently access these lists, leading to race conditions and crashes.
• A ScopedMutex class is used to automatically lock and unlock the mutex in various methods that access these lists.

This fix was generated by Seer in Sentry, triggered automatically. 👁️ Run ID: 2448566

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