Stored properties cannot be marked potentially unavailable with '@available' in AudioManager.swift (Swift 6.1/Xcode 16.4)

[Shultsie18]

To Reproduce
Steps to reproduce the behavior:

1. Add DeltaCore as a Swift Package dependency.
2. Build the project with Xcode 16.4 (Swift 6.1).
3. See the build error.

Expected behavior
The package should build successfully on all supported Swift/Xcode versions.

Environment:

• DeltaCore version: [your version or branch]
• Xcode version: 16.4
• Swift version: 6.1
• Platform: iOS/macOS

Additional context
This is not allowed in Swift 6.1 (and earlier):

@available(iOS 15, *)
var myProperty: SomeType // ❌ Not allowed on stored properties

@available can only be used on computed properties, functions, types, or extensions.

Suggested fix
Remove @available from stored properties, or refactor to use computed properties or type-level availability.

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Thank you for your work on DeltaCore!