docs+feat: add Disposable interface source and usage example

feat(core,doc): unified async dispose mechanism for resource cleanup

BREAKING CHANGE:

- Added full support for asynchronous resource cleanup via a unified FutureOr<void> dispose() method in the Disposable interface.
- The Scope now provides only Future<void> dispose() for disposing all tracked resources and child scopes (sync-only dispose() was removed).
- All calls to cleanup in code and tests (scope itself, subscopes, and custom modules) now require await ...dispose().
- Documentation and all examples updated: resource management is always async and must be awaited; Disposable implementers may use both sync and async cleanup.
- Old-style, synchronous cleanup methods have been completely removed (API is now consistently async for all DI lifecycle management).
- Example and tutorial code now demonstrate async resource disposal patterns.

cherrypick/example/disposable_example.dart

@@ -0,0 +1,40 @@
+import 'package:cherrypick/cherrypick.dart';
+
+/// Ваш сервис с освобождением ресурсов
+class MyService implements Disposable {
+  bool wasDisposed = false;
+
+  @override
+  void dispose() {
+    // Например: закрыть соединение, остановить таймер, освободить память
+    wasDisposed = true;
+    print('MyService disposed!');
+  }
+
+  void doSomething() => print('Doing something...');
+}
+
+void main() {
+  final scope = CherryPick.openRootScope();
+
+  // Регистрируем биндинг (singleton для примера)
+  scope.installModules([
+    ModuleImpl(),
+  ]);
+
+  // Получаем зависимость
+  final service = scope.resolve<MyService>();
+  service.doSomething(); // «Doing something...»
+
+  // Освобождаем все ресурсы
+  scope.dispose();
+  print('Service wasDisposed = ${service.wasDisposed}'); // true
+}
+
+/// Пример модуля CherryPick
+class ModuleImpl extends Module {
+  @override
+  void builder(Scope scope) {
+    bind<MyService>().toProvide(() => MyService()).singleton();
+  }
+}