Add is_semiconnected function.

[georgios-ts]

What is the expected enhancement?

A graph is semiconnected if, and only if, for any pair of nodes, either one is reachable from the other, or they are mutually reachable.

For reference, see https://networkx.org/documentation/stable/reference/algorithms/generated/networkx.algorithms.components.is_semiconnected.html#networkx.algorithms.components.is_semiconnected

For the implementation, we can consider adapting petgraph::condesation function https://docs.rs/petgraph/0.6.0/petgraph/algo/fn.condensation.html. We can't use it directly since it only works with petgraph::Graph but we have a petgraph::StableGraph as our underlying graph data structure.

[SECRETSTAR01]

Hey @georgios-ts !

Can you please tell where do we need to add this function, where are we going to use it ?