MAINT Decrease code diff and fix Cython-lint

[adam2392]

Reference Issues/PRs

When possible, I would prefer having a lower code diff on the scikit-learn fork since Github merge conflicts increase with each change. These are simply cosmetic changes that keep the original code where it was unless there is a change that seems necessary.

• split functions are just kept in splitter.pyx
• split functions are importable by adding to the splitter.pxd

What does this implement/fix? Explain your changes.

Any other comments?

[github-actions]

❌ Linting issues

There was an issue running the linter job. Please update with upstream/main (link) and push the changes. If you already have done that, please send an empty commit with git commit --allow-empty and push the changes to trigger the CI.

_{Generated for commit: b039520. Link to the linter CI: here}

[SamuelCarliles3]

I broke out the sort functions into their own module because

• they're used both by Splitter and by Partitioner
• Splitter depends on Partitioner
• as a practice, circular dependencies are best avoided, so that Partitioner should then not depend on Splitter
• more generally, dependency graphs are best modeled as DAGs

[adam2392]

Hmm fair point. Let me try to circle this up with scikit learn devs to try to make the code more maintainable.