Replace blockdiag

[Dreamsorcerer]

In docs/tracing_reference.rst we use blockdiag to create some diagrams. The project is unmaintained now and causing issues upgrading to latest versions of sphinx.

We need someone to replace these diagrams with an alternative. In the Sphinx documentation, they recommend GraphViz: https://chiplicity.readthedocs.io/en/latest/Using_Sphinx/UsingGraphicsAndDiagramsInSphinx.html

So, the blockdiag statements need to be replaced with graphviz ones.

[webknjaz]

I'd look into https://pypi.org/p/sphinx-mermaid

[shirsakm]

Hi, I would like work on this issue, but I would need some guidance. Would that be okay?

[Dreamsorcerer]

Go ahead. Let us know if you have questions.

[Cycloctane]

Note that sphinx built-in extension sphinx.ext.graphviz requires graphviz executable (dot) to render diagrams. (https://www.sphinx-doc.org/en/master/usage/extensions/graphviz.html#confval-graphviz_dot)
I think if we prefer GraphViz, we may also update contributing.rst to mention this additional requirement in documentation build instructions.

[Dreamsorcerer]

Personally, I don't mind what is used, as long as it works. If someone wants to take it on, use whatever you want.

I'd note that sphinx-mermaid appears to be about as abandoned as blockdiag, so I'm thinking that graphviz is probably a safer bet.