message: Fix import order in `memory_metrics`
diff: use datasize::DataSize;
  use prometheus::{exponential_buckets, Histogram, HistogramOpts, IntGauge, Registry};
  use rand::{CryptoRng, Rng};
  +use tracing::debug;
  use super::Reactor;
  -use tracing::debug;
  /// Metrics for memory usage.
  #[derive(Debug)]
  