feat：参照研听的基础工程

lib/common/domain/money.dart

@@ -0,0 +1,11 @@
+String formatCny(num value) {
+  final fixed = value.toStringAsFixed(2);
+  final parts = fixed.split('.');
+  final whole = parts.first.replaceAllMapped(
+    RegExp(r'(\d)(?=(\d{3})+(?!\d))'),
+    (match) => '${match[1]},',
+  );
+  return '¥$whole.${parts.last}';
+}
+
+String formatGram(num value) => '${value.toStringAsFixed(2)}g';