need graphviz

[loriab]

Description

• I strongly suspect this'll fix Class inheritance diagram not rendering #333 which wasn't working b/c dot not present b/c it can't be installed by pypi. (Can be installed thru conda.) Fortunately there's a GHA action to the rescue.
• Missing class docstrings were generating ERROR: Content block expected for the "raw" directive; none found.
• the unescaped qc_ were being interpreted as sphinx links
• I don't think there's harm in importing nglview with forgiveness. It's the only way the docs build can recognize the forward reference.
• there's still many (15) duplicate object description warnings, but I'll defer those

Changelog description

Status

• Code base linted
• Ready to go