[BUG] Remove pdb breakpoint and make single-op-splits robust to 1d shape

[ibevers]

Types of changes

• Bug fix (non-breaking change which fixes an issue)

Summary

Removes a stray pdb breakpoint and makes the splitter functionality robust to 1D inputs for singleton splitters.

Checklist

I will add a test for this case.

• [ ] I have added tests to cover my changes (if necessary)
• [x] I have updated documentation (if necessary)