Method CreateWriter

src/data/sparse_page_source.h:198–200

 public:
  std::unique_ptr<WriterT> CreateWriter(StringView name, std::uint32_t iter) {
    return DftCreateWriterImpl<WriterT>(name, iter);
  }

  std::unique_ptr<ReaderT> CreateReader(StringView name, std::uint64_t offset,
                                        std::uint64_t length) const {