Tests: Add test for case-insensitive topic headers

Add test case in the commit to verify that message list topic headers handle
case-insensitive topic comparison correctly, ensuring messages with
topics that differ only in case (like "hello world" and "Hello World")

test/model/message_list_test.dart

@@ -1703,6 +1703,23 @@ void main() {
         }
       }
     });
+    test('stream messages match with case-insensitive topics', () {
+      final stream = eg.stream();
+      final messageLower = eg.streamMessage(
+          stream: stream,
+          topic: 'hello world');
+      final messageUpper = eg.streamMessage(
+          stream: stream,
+          topic: 'Hello World');
+      final messageDiff = eg.streamMessage(
+          stream: stream,
+          topic: 'different');
+
+      check(haveSameRecipient(messageLower, messageUpper)).isTrue();
+      check(haveSameRecipient(messageUpper, messageLower)).isTrue();
+      check(haveSameRecipient(messageLower, messageDiff)).isFalse();
+      check(haveSameRecipient(messageUpper, messageDiff)).isFalse();
+    });
   });
 
   test('messagesSameDay', () {