refactor: rename benchmark_cherrypick to benchmark_di, update paths, pubspec, imports, and documentation

benchmark_di/lib/scenarios/universal_service.dart

@@ -0,0 +1,17 @@
+
+/// Base interface for any universal service in the benchmarks.
+///
+/// Represents an object in the dependency chain with an identifiable value
+/// and (optionally) a dependency on a previous service in the chain.
+abstract class UniversalService {
+  /// String ID for this service instance (e.g. chain/level info).
+  final String value;
+  /// Optional reference to dependency service in the chain.
+  final UniversalService? dependency;
+  UniversalService({required this.value, this.dependency});
+}
+
+/// Default implementation for [UniversalService] used in service chains.
+class UniversalServiceImpl extends UniversalService {
+  UniversalServiceImpl({required super.value, super.dependency});
+}