Adopted Span and MutableSpan for buffers across the library to adapt to Swift 6.4.

Sources/PlaydateKit/Sound/Sound.swift

@@ -51,14 +51,14 @@ extension Sound {
 
     /// Sets a callback that records microphone input. Return `false` from the
     /// callback to stop recording. Pass `nil` to stop recording immediately.
-    /// The buffer contains mono 16-bit samples.
+    /// The span contains mono 16-bit samples.
     @discardableResult
     public static func setMicCallback(source: MicSource = .autodetect,
-                                      _ callback: ((UnsafeMutableBufferPointer<Int16>) -> Bool)?) -> Bool {
+                                      _ callback: ((Span<Int16>) -> Bool)?) -> Bool {
         micCallback = callback
         if callback != nil {
             return snd.pointee.setMicCallback.unsafelyUnwrapped({ _, buffer, length in
-                let samples = UnsafeMutableBufferPointer(start: buffer, count: Int(length))
+                let samples = UnsafeBufferPointer(start: buffer, count: Int(length)).span
                 return Sound.micCallback?(samples) == true ? 1 : 0
             }, nil, CPlaydate.MicSource(CPlaydate.MicSource.RawValue(source.rawValue))) != 0
         } else {
@@ -66,7 +66,7 @@ extension Sound {
         }
     }
 
-    nonisolated(unsafe) private static var micCallback: ((UnsafeMutableBufferPointer<Int16>) -> Bool)?
+    nonisolated(unsafe) private static var micCallback: ((Span<Int16>) -> Bool)?
 
     /// Asks the user for permission to record from the microphone. `purpose`
     /// is shown in the permission prompt. The completion receives whether