message: storage: user unstable sort to reduce memory allocation
  We can bear with non-ordered equal elements when sorting.
diff: @@ -456,7 +456,7 @@ impl BlobCache for FileCacheEntry {
  // Then handle fs prefetch
  let max_comp_size = self.prefetch_batch_size();
  let mut bios = bios.to_vec();
  - bios.sort_by_key(|entry| entry.chunkinfo.compressed_offset());
  + bios.sort_unstable_by_key(|entry| entry.chunkinfo.compressed_offset());
  self.metrics.prefetch_unmerged_chunks.add(bios.len() as u64);
  BlobIoMergeState::merge_and_issue(
  &bios,
  