gh-103978: avoid using 'class' as an identifier

[carljm]

fixes #103978

• Issue: 'class' parameter name in headers breaks building C++ extensions #103978

[brandtbucher]

Super, super minor... but maybe use cls instead of klass for this?

It's a much more common name in our codebase... and I personally like it a lot more. 🙃

[tacaswell]

Thank you!