tfardet/NNGT: NNGT 2.3.0: improved (undirected) analysis and plots

This new release includes a lot of bugfixes and under-the-hood improvements as well as a set of new tools for better analysis, especially with undirected measures.

All testing and main code hosting has been moved to SourceHut and the documentation has been updated and now includes an automatic dark theme for all browser requesting it.

• to_undirected method, to create undirected counterparts from directed (even weighted) networks (patch 20376)
• local_closure as a complementary tool for clustering (#155), see [Yin2019]
• Zhang--Horvath method for weighted clustering (#146), see [Zhang2005]

• improved support for positions/structures (#149)
• improved from_matrix class method to support all Graph arguments (#149)
• improved plots: positional layout and opacity (#149):
  • layout can now be a list of custom positions.
  • added ealpha and nalpha support for edge and node transparency.
• shortest path and path length method can be used in "undirected" mode on directed weighted networks (patch 20470)

• corrected calculation of weighted path length for SWP (patch 20470)
• fixed circular graph and lattice reciprocity (patch 20412)
• corrected spatial plots with networkx (#154)
• fixed IO issue with non-string node attributes (#152)
• fixed nonstring_container import for RNGs (#151)
• fixed edge deletion with nngt backend (#149)

Default mode for SWP is now to use the average local clustering instead of the global clustering.