HDDS-16215. Avoid the per-group list copy in OmMetadataManagerImpl.getBlocksForKeyDeletetBlocksForKeyDelete

[orca-07]

What changes were proposed in this pull request?

getBlocksForKeyDelete flatten-copies each version group only to stream it once into DeletedBlock items:

      for (OmKeyLocationInfoGroup keyLocations :
          info.getKeyLocationVersions()) {
        List<DeletedBlock> item = keyLocations.createLocationList().stream()
            .map(b -> new DeletedBlock(
                new BlockID(b.getContainerID(), b.getLocalID()),
                b.getLength(),
                QuotaUtil.getReplicatedSize(b.getLength(), info.getReplicationConfig()),
                QuotaUtil.getSizePerReplica(b.getLength(), info.getReplicationConfig())))
            .collect(Collectors.toList());
        BlockGroup keyBlocks = BlockGroup.newBuilder()
            .setKeyName(deletedKey)
            .addAllDeletedBlocks(item)
            .build();
        result.add(keyBlocks);
      }

Fix: keyLocations.getLocationLists().stream().flatMap(List::stream). Behavior unchanged.

What is the link to the Apache JIRA

https://issues.apache.org/jira/browse/HDDS-16215

How was this patch tested?

https://github.com/orca-07/ozone/actions/runs/32567086538

[F64116045]

LGTM, thanks @orca-07 for the patch.

[chungen0126]

Thanks @orca-07 for working on this. It would be better to have a micro benchmark.