feat(extensions): add string truncate functionality

- Implement StringTruncate extension to truncate strings to a specified maximum length
- Add new exports for source_type_l10n.dart and string_truncate.dart in extensions.dart

Author: fulleni

lib/shared/extensions/extensions.dart

@@ -1 +1,3 @@
 export 'content_status_l10n.dart';
+export 'source_type_l10n.dart';
+export 'string_truncate.dart';

lib/shared/extensions/string_truncate.dart

@@ -0,0 +1,8 @@
+extension StringTruncate on String {
+  String truncate(int maxLength) {
+    if (length <= maxLength) {
+      return this;
+    }
+    return '${substring(0, maxLength)}...';
+  }
+}