feat: support custom tracker url (#59)

ui/flutter/lib/widget/outlined_button_loading.dart

@@ -0,0 +1,52 @@
+import 'package:flutter/material.dart';
+
+class OutlinedButtonLoading extends StatefulWidget {
+  final Widget child;
+  final VoidCallback onPressed;
+  final OutlinedButtonLoadingController controller;
+
+  const OutlinedButtonLoading(
+      {super.key,
+      required this.child,
+      required this.onPressed,
+      required this.controller});
+
+  @override
+  State<OutlinedButtonLoading> createState() => _OutlinedButtonLoadingState();
+}
+
+class _OutlinedButtonLoadingState extends State<OutlinedButtonLoading> {
+  @override
+  Widget build(BuildContext context) {
+    return ValueListenableBuilder<bool>(
+      valueListenable: widget.controller,
+      builder: (context, value, child) {
+        return OutlinedButton(
+          key: widget.key,
+          onPressed: value ? null : widget.onPressed,
+          child: value
+              ? const SizedBox(
+                  height: 20,
+                  width: 20,
+                  child: CircularProgressIndicator(
+                    strokeWidth: 2,
+                  ),
+                )
+              : widget.child,
+        );
+      },
+    );
+  }
+}
+
+class OutlinedButtonLoadingController extends ValueNotifier<bool> {
+  OutlinedButtonLoadingController() : super(false);
+
+  void start() {
+    value = true;
+  }
+
+  void stop() {
+    value = false;
+  }
+}