Bugs in vertex ordering algorithms.

[samuelsonric]

The tests for the FlowCutter algorithm pass on my computer, but error (sometimes) when run by GitHub actions. FlowCutter is returning an empty file. Those tests are currently commented out.

[samuelsonric]

The Spectral ordering fails on singleton graphs due to an upstream bug in Laplacians.jl. That test is currently commented out.

[jpfairbanks]

I didn't know about that package, but should be easy to patch upstream since there is only one ordering for the singleton graph!

[samuelsonric]

The tests for the FlowCutter algorithm pass on my computer, but error (sometimes) when run by GitHub actions. FlowCutter is returning an empty file. Those tests are currently commented out.

Removed this algorithm for now.