timing information added in debugprint

I'm not sure it's optimally efficient yet. The problem is values in `total_times` are set in `compute_total_times`, and not in `get_node_total_time`, which means that you won't put the total time of a node's parent in `total_times` until it's been  iterated over in `compute_total_times`.

Here's my suggestion: instead of returning the total time for a given node, this method should directly set the total time in `total_times` and return nothing. You could rename it to something like `fill_node_total_time` to make it clearer that nothing is returned.