message: fix string conversion of DType enums
diff: @@ -108,6 +108,8 @@ inline const char* to_string(DType dtype) {
  case DType::UINT32:
  return "uint32";
  case DType::INT64:
  + return "int64";
  + case DType::UINT64:
  return "uint64";
  case DType::BFLOAT16:
  return "bfloat16";
  