incorrect 'node already registered' error when two nodes have the same name (but are from different modules)

Describe the bug

I have a sphinx extension that defines two different custom directives and registers corresponding custom docutils Nodes. Each custom node is called Node, but is namespaced by it's respective module, like so-

• module_a.Node
• module_b.Node

when running a build, i get an error-

WARNING: while setting up extension ${EXTENSION}: node class 'Node' is already registered, its visitors will be overridden

looking at the code in sphinx.util.docutils.is_node_registered I can see that nodes are registered by their class name only (cls.__name__), and not by their qualified names (cls.__qualname__). Hence you get erroneous collisions if two classes in different modules have the same name.

How to Reproduce

(you'll need Poetry installed)

git clone https://github.com/danieleades/sphinx-graph
cd sphinx-graph
git checkout table
cd docs
poetry run make html
# observe the error

i've also created a minimal reproduction here - https://github.com/danieleades/sphinx-bug-11220

Start with sphinx.util.docutils.is_node_registered and trace how custom nodes are registered during extension setup. Use the linked minimal reproduction or the sphinx-graph reproduction to verify the behavior for module_a.Node and module_b.Node, then add or update tests so distinct module classes no longer produce a duplicate-registration warning.