Should is_distance_regular and intersection_array have @not_implemented_for?

[rossbar]

Something I noticed while reviewing #5849 :

The docstrings for is_distance_regular and intersection_array state that they are only defined for undirected graphs; however, the implementations do not check the type of the graph. The functions and definitions should be reviewed to determine whether these should get the not_implemented_for decorator.

[dschult]

It looks like those two functions use @not_implemented_for("directed", "multigraph") which is almost certainly a bug that should be written:

@not_implemented_for("directed")
@not_implemented_for("multigraph")

See #6904 for others that should be checked too.