Experiment with using `GraphBLAS`

[luke-kiernan]

The PNM equivalent of PF #194. There's several cases of graph-math-via-matrix-math here:

• Identify radial chains
• Identify degree 2 chains
• Compute an incidence or adjacency matrix via iterating over the Ybus
• Find connected components via DFS or BFS [low-priority because union-find is likely faster]

I suspect we could do many of these things with GraphBLAS: see this DFS example on Wikipedia.