Add total_nodes method to TreeMeshes

[santisoler]

The new method returns the whole set of nodes in the mesh, including non-hanging and hanging nodes. It comes useful when working together with cell_nodes.

[jcapriot]

This should probably be called total_nodes to follow the naming convention already in the tree mesh: nodes, hanging_nodes, n_nodes, n_hanging_nodes and n_total_nodes.

[santisoler]

I agree that it should follow the convention used on the other methods, so I think it's better to rename it.

Nevertheless, I think is nice to name things like nodes_all, nodes_hanging, nodes_non_hanging for easier discoverability: they'll be listed together in the docs, users can use tab completion to explore what properties and methods are available for nodes.... Just mentioning to keep it in mind for the future.

[codecov]

Codecov Report

Merging #324 (327ccc2) into main (ee39262) will increase coverage by 0.00%.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #324   +/-   ##
=======================================
  Coverage   85.15%   85.16%           
=======================================
  Files          38       38           
  Lines       11535    11538    +3     
=======================================
+ Hits         9823     9826    +3     
  Misses       1712     1712           

Impacted Files	Coverage Δ
discretize/_extensions/tree_ext.pyx	84.44% <ø> (ø)
discretize/tree_mesh.py	71.19% <100.00%> (+0.20%)	⬆️

[jcapriot]

n_total_nodes