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/Graphics/Structures/Bitmap.Data.swift

@@ -1,18 +1,12 @@
 extension Graphics.Bitmap {
-    /// The bitmap's dimensions, row stride, and raw pixel/mask storage.
-    /// The pointers are owned by the bitmap.
-    public struct Data {
-        /// The bitmap's width, in pixels.
+    /// A bitmap's layout. Read pixels with `withPixelData(_:)` and `withMaskData(_:)`.
+    public struct Data: Sendable {
+        /// Width, in pixels.
         public let width: Int
-        /// The bitmap's height, in pixels.
+        /// Height, in pixels.
         public let height: Int
-        /// The stride of one row of pixel data, in bytes.
+        /// Row stride of the pixel and mask data, in bytes.
         public let rowBytes: Int
-        /// The bitmap's mask data, or `nil` if it has no mask. One bit per
-        /// pixel; rows are `rowBytes` wide.
-        public let mask: UnsafeMutablePointer<UInt8>?
-        /// The bitmap's pixel data. One bit per pixel; rows are `rowBytes`
-        /// wide.
-        public let data: UnsafeMutablePointer<UInt8>?
+        public let hasMask: Bool
     }
 }