Node::diff comparison failure

First off, I don't have a good reproducer for this but I want to mention it anyway. When making the partitioner and now with the TopologyMetadata test case, I found it was necessary to either implement my own Node comparison function or introduce other workarounds.

Sometimes Node::diff will indicate that nodes are equal when they are not equal.

Most recently, this came up in the TopologyMetadata CI test case where it turns the TopologyMetadata into a Node (with lots of subtrees) and I found that when I compared my in-memory Node vs one read from relay, they would compare as equal according to Node::diff. When making a CI test case, this is great - you think you're good because there were no differences. I found through other means though that some of my maps were wrong and this should have been flagged by Node::diff. I came up with a workaround in the compare_baseline() function where I can write my in-memory node to a file, read it back, and then compare against the read-in baseline and then Node::diff shows any differences reliably.

The nodes that failed to compare properly were arrays of index_t.

Start by examining Node::diff and the TopologyMetadata CI test case, including the compare_baseline() workaround described in the issue. Focus on cases involving arrays of index_t; done means reliably detecting differences between in-memory and relayed nodes, with a regression test for the failure.