add parameter immutable to distance regular graph generators (part 5)

[dcoudert]

Following discussions in #39177, we add the option to return immutable graphs to some generators in src/sage/graphs/generators/distance_regular.pyx.

• graph_with_classical_parameters, pseudo_partition_graph, near_polygon_graph

We also add parameter immutable to methods project_left and project_right of BipartiteGraph and to method folded_graph of Graph.

After that, it remains only method distance_regular_graph in src/sage/graphs/generators/distance_regular.pyx.

📝 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 a541ad2; changes) is ready! 🎉
This preview will update shortly after each push to this PR.