doc: added comments to code

cherrypick_annotations/lib/src/named.dart

@@ -1,5 +1,31 @@
+/// An annotation to assign a name or identifier to a class, method, or other element.
+///
+/// This can be useful for code generation, dependency injection,
+/// or providing metadata within a framework.
+///
+/// Example:
+/// ```dart
+/// @module()
+/// abstract class AppModule extends Module {
+///   @named('dio')
+///   Dio dio() => Dio();
+/// }
+/// ```
+///
+/// Сгенерирует код:
+/// ```dart
+/// final class $AppModule extends AppModule {
+///   @override
+///   void builder(Scope currentScope) {
+///     bind<Dio>().toProvide(() => dio()).withName('dio').singleton();
+///   }
+/// }
+/// ```
 // ignore: camel_case_types
-class named {
+final class named {
+  /// The assigned name or identifier.
   final String value;
+
+  /// Creates a [named] annotation with the given [value].
   const named(this.value);
 }