add methods for biconnected components

[dcoudert]

This PR do the following:

• add method number_of_biconnected_components to follow the proposal of n_nodes and number_of_nodes_xxx in tree related classes #40939
• add method biconnected_components
• move method is_biconnected from graph.py to connectivity.pyx and expose it in generic_graph.pyx

The addition of method biconnected_component_containing_vertex is more involved and deserves its own PR. Indeed, a cut vertex belongs to multiple biconnected components.

📝 Checklist

• The title is concise and informative.
• The description explains in detail what this PR is about.
• I have linked a relevant issue or discussion.
• I have created tests covering the changes.
• I have updated the documentation and checked the documentation preview.

⌛ Dependencies

[github-actions]

Documentation preview for this PR (built with commit 196151d; changes) is ready! 🎉
This preview will update shortly after each push to this PR.

[mantepse]

Looks right!

Mathematically, it is correct that the union of the components is not the full graph, right?

[dcoudert]

Mathematically, it is correct that the union of the components is not the full graph, right?

Here we consider the union of the biconnected components of the graph. So if a component is not biconnected (i.e., the graph has an isolated vertex), then the union of the biconnected components is not the full graph.

Also, all the methods about biconnected components are consistent and recall the definition that a component is biconnected if it remains connected after the removal of any vertex. A component consisting of a single edge is therefore considered biconnected. This is a corner case. In case a user prefers components with 3 or more vertices it is possible to filter the results.

Thanks for the review.