The existing algorithm was a little too fragile and dependent on
branch numbers. This new version starts at segment 1/branch 1 and
follows Segment::inletSegments() in depth-first order, taking care
to enqueue new branches as they're encountered instead of in
numerical order. We search to the end of each branch before
switching to the next branch. This ensures determinism regardless
of branch numbering and input ordering.
While here, switch iLBR_ to a WindowedMatrix<int> to simplify branch
references in the output table.
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