protected Collection<NR> getNodeChildrenOf(NR parent) {
		return cachedNodeChildren.computeIfAbsent(parent.getKey(),
			k -> new ArrayList<>(getNodeChildrenOf(k)));
	}
For non-leaf nodes, get the children.

For leaf nodes, the behavior is undefined. Note that the query should not filter the
children, only order them, or else the collection will return an incorrect
{@link Collection#size()}. Filtering is performed by {@link TreeRecordVisitor}.

@param parent the parent node
@return a collection of the children
Ghidra/Debug/ProposedUtils/src/main/java/ghidra/util/database/spatial/AbstractConstraintsTree.java