Possible bug in collecting performance data

Hello All,

When collecting performance data, current implementation assumes from_sep_close_bigger is indexed like target_boxes, but the documentation says it should indexed like target_or_target_parent_boxes.

Relevant code: https://gitlab.tiker.net/inducer/pytential/blob/master/pytential/qbx/fmm.py#L716

Relevant doc: https://documen.tician.de/boxtree/traversal.html#boxtree.traversal.FMMTraversalInfo.from_sep_close_bigger_starts