feat: always return true for unspported platforms

Author: mcquenji

lib/src/unsupported.dart

@@ -0,0 +1,16 @@
+import 'dart:io';
+
+import 'package:flutter_single_instance/flutter_single_instance.dart';
+
+class FlutterSingleInstanceUnsopported extends FlutterSingleInstance {
+  const FlutterSingleInstanceUnsopported() : super.internal();
+
+  @override
+  Future<String?> getProcessName(int pid) async => null;
+
+  @override
+  Future<bool> isFirstInstance() async => true;
+
+  @override
+  Future<File?> getPidFile(String processName) async => null;
+}