Class is_polymorphic

cpp/fory/serialization/serializer_traits.h:295–295

/// For smart pointers (shared_ptr, unique_ptr), they are polymorphic if their
/// element type is polymorphic, matching Rust's Rc<dyn Trait> behavior.
template <typename T> struct is_polymorphic : std::is_polymorphic<T> {};

// Smart pointers are polymorphic if their element type is polymorphic
// This matches Rust's Rc<dyn Trait> / Arc<dyn Trait> behavior