Swift 6.4 migration and exhancements (#1)

This PR contains the work done to update the library and the attached example project to use the Swift 6.4 computer as a minimum supported version and also, to use the latest features introduced in it.

Reviewed-on: #1
Co-authored-by: Javier Cicchelli <javier@rock-n-code.com>

Sources/PlaydateKit/Sound/Effect/Classes/DelayLine.swift

@@ -5,7 +5,7 @@ extension Sound {
     public final class DelayLine: Effect {
         private static var api: UnsafePointer<playdate_sound_effect_delayline> { Playdate.delayLineAPI.unsafelyUnwrapped }
 
-        /// Creates a delay line holding `length` frames.
+        /// `length` is in frames.
         public init(length: Int, stereo: Bool = false) {
             super.init(pointer: DelayLine.api.pointee.newDelayLine.unsafelyUnwrapped(
                 Int32(length), stereo ? 1 : 0).unsafelyUnwrapped, isOwned: true)
@@ -17,19 +17,18 @@ extension Sound {
             }
         }
 
-        /// Changes the delay length. Cannot be larger than the line's
-        /// original length.
+        /// Clears the buffer and reallocates, so not safe while the line is in use.
         public func setLength(frames: Int) {
             DelayLine.api.pointee.setLength.unsafelyUnwrapped(pointer, Int32(frames))
         }
 
-        /// The feedback level, 0...1.
+        /// 0...1.
         public func setFeedback(_ feedback: Float) {
             DelayLine.api.pointee.setFeedback.unsafelyUnwrapped(pointer, feedback)
         }
 
-        /// Adds a tap `delay` frames behind the write head. The tap can be
-        /// added to a channel as a sound source.
+        /// `delay` is in frames behind the write head, at most the line's length.
+        /// The tap keeps the line alive.
         public func addTap(delay: Int) -> DelayLineTap? {
             guard let tap = DelayLine.api.pointee.addTap.unsafelyUnwrapped(pointer, Int32(delay)) else {
                 return nil