Update ffi package dependency

[shaxxx]

Currently, using this package as dependency causes compile error

Launching lib/main.dart on macOS in debug mode...
lib/main.dart:1
../lib/src/quick_usb_desktop.dart:110:38: Error: Expected type 'Utf8' to be a valid and instantiated subtype of 'NativeType'.
 - 'Utf8' is from 'package:ffi/src/utf8.dart' ('../../../../.pub-cache/hosted/pub.dartlang.org/ffi-1.1.2/lib/src/utf8.dart').

Offending line is

Pointer<ffi.Utf8> string = ffi.malloc(256);

Seems this is known issue
flutter/flutter#76705

To resolve it, ffi package dependency needs to be updated to latest version (currently 1.1.2)

[Sunbreak]

Since dart-lang/sdk#44622, Utf8 is subclass of Opaque, which is designed to be uninstantiatable

/// [Opaque]'s subtypes represent opaque types in C.
///
/// [Opaque]'s subtypes are not constructible in the Dart code and serve purely
/// as markers in type signatures.
abstract class Opaque extends NativeType {}

Use Uint8 instead

Pointer<ffi.Utf8> pointer = ffi.malloc<Uint8>(256).cast();