REF: Groupby._get_cythonized_result operate blockwise in axis==1 case
- [ ] closes #xxxx
- [ ] tests added / passed
- [ ] Ensure all linting tests pass, see [here](https://pandas.pydata.org/pandas-docs/dev/development/contributing.html#code-standards) for how to run them
- [ ] whatsnew entry

needs a rebase, b ut i think you have changed a bunch of this code rebased + green is this a bug fix? or just perf on a case? > is this a bug fix? or just perf on a case?

Neither, just going from 2 paths to 1 path.