Fix multiple critical bugs: thread safety, memory leaks, null references, and async patterns

[Copilot]

This PR addresses multiple critical bugs and stability issues in the ScreenSoundSwitch application that could cause crashes, memory leaks, and unexpected behavior.

Key Issues Fixed

1. Thread Safety Violations

Fixed non-thread-safe singleton implementations in ScreenToAudioDevice and AudioDeviceManager that could cause race conditions:

// Before: Race condition possible
public static AudioDeviceManager Instance => _instance ??= new AudioDeviceManager();

// After: Thread-safe double-checked locking
public static AudioDeviceManager Instance
{
    get
    {
        if (_instance == null)
        {
            lock (_lock)
            {
                if (_instance == null)
                    _instance = new AudioDeviceManager();
            }
        }
        return _instance;
    }
}

2. Memory Leaks and Resource Management

Implemented proper IDisposable patterns with finalizers to prevent COM object leaks:

public void Dispose()
{
    Dispose(true);
    GC.SuppressFinalize(this);
}

protected virtual void Dispose(bool disposing)
{
    if (!_disposed && disposing)
    {
        _enumerator?.UnregisterEndpointNotificationCallback(_notificationClient);
        _enumerator?.Dispose();
        _disposed = true;
    }
}

3. Volume Bounds Validation

Added critical bounds checking to prevent invalid audio volume values that could cause audio driver issues:

public void ChangeSimpleVolumeLevel(float level)
{
    if (session?.SimpleAudioVolume == null) return;
    
    var newVolume = session.SimpleAudioVolume.Volume + level;
    // Ensure volume stays within valid range [0.0, 1.0]
    newVolume = Math.Max(0.0f, Math.Min(1.0f, newVolume));
    session.SimpleAudioVolume.Volume = newVolume;
}

4. Async/Await Anti-patterns

Fixed dangerous async void methods and synchronous file access that could deadlock the UI:

// Before: Potential deadlock
ViewModel.SetAudioFileFolder(StorageFolder.GetFolderFromPathAsync(path).AsTask().Result);

// After: Proper async handling
var folder = await StorageFolder.GetFolderFromPathAsync(audioFilePath);
ViewModel?.SetAudioFileFolder(folder);

5. Null Reference Protection

Added comprehensive null checks throughout the application, particularly in process and audio session handling:

public bool IsScreenChange(Screen screen)
{
    if (screen == null) return false;
    if (this.screen == null || !this.screen.Equals(screen))
    {
        this.screen = screen;
        return true;
    }
    return false;
}

Additional Improvements

• Application Title: Fixed typo "ScreenSoundSwicth" → "ScreenSoundSwitch"
• Error Handling: Added try-catch blocks around all critical operations with detailed logging
• Process Validation: Enhanced process handle validation before screen detection
• Event Handler Safety: Protected all event handlers from unhandled exceptions
• Resource Disposal: Proper cleanup of icons, streams, and COM objects
• Dictionary Initialization: Fixed uninitialized collections that could cause NullReferenceException

Impact

These fixes significantly improve application stability by:

• Preventing crashes from null reference exceptions
• Eliminating memory leaks from undisposed COM objects
• Avoiding audio driver issues from invalid volume values
• Preventing UI freezing from synchronous file operations
• Ensuring thread safety in multi-threaded scenarios

The application should now run more reliably in production environments with proper error recovery and resource management.

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