The cold standby client doesn't correctly handle backward references

The logic from StandbyClientSyncExecution#copySegmentHierarchyFromPrimary has a flaw when it comes to "backward references". Suppose we have the following data segment graph to be transferred from primary: S1, which references {S2, S3} and S3 which references S2. Then, the correct transfer order should be S2, S3 and S1.

Going through the current logic employed by the method, here's what happens:

Step 0: batch={S1}

Step 1: visited={S1}, data={S1}, batch={S2, S3}, queued={S2, S3}

Step 2: visited={S1, S2}, data={S2, S1}, batch={S3}, queued={S2, S3}

Step 3: visited={S1, S2, S3}, data={S3, S2, S1}, batch={}, queued={S2, S3}.

Therefore, at the end of the loop, the order of the segments to be transferred will be S3, S2, S1, which might trigger a SegmentNotFoundException when S3 is further processed, because S2 is missing on standby (see OAK-8006).

/cc frm