message: Avoid unused warning for DB_READ_KEY_BUFFER_LENGTH
diff: @@ -15,6 +15,7 @@ use crate::types::{CanonicalAddr, HumanAddr};
  /// A kibi (kilo binary)
  static KI: usize = 1024;
  /// The number of bytes of the memory region we pre-allocate for the result data in ExternalIterator.next
  +#[cfg(feature = "iterator")]
  static DB_READ_KEY_BUFFER_LENGTH: usize = 64 * KI;
  /// The number of bytes of the memory region we pre-allocate for the result data in ExternalStorage.get
  /// and ExternalIterator.next
  