feat: build windows dll and call dll in flutter

ui/lib/ffi/backend.dart

@@ -0,0 +1,41 @@
+import 'dart:ffi';
+import 'dart:io';
+import 'dart:isolate';
+
+import 'package:ui/widgets/utils.dart' as Utils;
+
+
+class FFIBackend {
+  final lib = DynamicLibrary.open(libname());
+
+  static String libname() {
+    if (Utils.isDesktop()) {
+      if (Platform.isWindows) {
+        return 'libpolaris.dll';
+      } else if (Platform.isLinux) {
+        return 'libpolaris.so';
+      } else if (Platform.isMacOS) {
+        return 'libpolaris.dylib';
+      } else {
+        throw UnsupportedError(
+            'Unsupported platform: ${Platform.operatingSystem}');
+      }
+    } else {
+      return "";
+    }
+  }
+
+  Future<void> start() async {
+    var s = lib
+        .lookup<NativeFunction<Void Function()>>('Start')
+        .asFunction<void Function()>();
+        
+    return Isolate.run(s);
+  }
+  Future<void> stop() async {
+    var s = lib
+        .lookup<NativeFunction<Void Function()>>('Stop')
+        .asFunction<void Function()>();
+    return s();
+  }
+}