tests: add chat model tests(cv: 100)

test/dashbot/models/chat_response_model_test.dart

@@ -0,0 +1,27 @@
+import 'package:apidash/dashbot/core/constants/constants.dart';
+import 'package:apidash/dashbot/features/chat/models/chat_response.dart';
+import 'package:test/test.dart';
+
+void main() {
+  group('ChatResponse equality & copyWith', () {
+    test('equality & hashCode', () {
+      const r1 =
+          ChatResponse(content: 'Hi', messageType: ChatMessageType.general);
+      const r2 =
+          ChatResponse(content: 'Hi', messageType: ChatMessageType.general);
+      expect(r1, r2);
+      expect(r1.hashCode, r2.hashCode);
+      expect(r1.toString(), contains('ChatResponse'));
+    });
+
+    test('copyWith modifies only provided fields', () {
+      const r1 = ChatResponse(content: 'One');
+      final r2 = r1.copyWith(content: 'Two');
+      expect(r2.content, 'Two');
+      expect(r2.messageType, isNull);
+      final r3 = r2.copyWith(messageType: ChatMessageType.generateCode);
+      expect(r3.messageType, ChatMessageType.generateCode);
+      expect(r3.content, 'Two');
+    });
+  });
+}