Update wuffs bindings to avoid alloations

pkg/wuffs/src/main.zig

@@ -7,7 +7,7 @@ pub const swizzle = @import("swizzle.zig");
 pub const ImageData = struct {
     width: u32,
     height: u32,
-    data: []const u8,
+    data: []u8,
 };
 
 test {

src/renderer/OpenGL.zig

@@ -1242,7 +1242,7 @@ pub fn prepBackgroundImage(self: *OpenGL, path: []const u8) !void {
     const pending: Image.Pending = .{
         .width = decoded_image.width,
         .height = decoded_image.height,
-        .data = @constCast(decoded_image.data).ptr,
+        .data = decoded_image.data.ptr,
     };
 
     // Store the image