Network reductions and constraint duals

[luke-kiernan]

Quoting from IOM's add_constraint_dual.jl in an about-to-be-merged PR:

Reuse the existing constraint container's row axis so the dual axis
matches the constraint exactly. Network reductions (radial /
degree-two) drop branches that pass the device-model filter, so the
constraint axis is a strict subset of IS.get_name.(devices). Sizing
the dual from the device list would leave the dual broadcast in
process_duals incompatible with the constraint matrix.

Add a dedicated test case for that.