Row-wise Mode Functionality (Dask Issue #11389)

I conducted a brief search to confirm if this has already been opened here.

Dask Issue [#11389 ](https://github.com/dask/dask/issues/11389) requested the addition of row-wise mode functionality for DataFrames. Through extensive research and testing, I found that the necessary modifications had to be made within dask_expr/_collection.py in the dask-expr repository.

I’m submitting this issue to formally document the need for these changes, and I plan to submit a PR shortly to support this. The code changes are already complete and have been thoroughly tested locally—PR submitted, pending approval.

Start in dask_expr/_collection.py, which the issue identifies as the location for the row-wise DataFrame mode changes. Review the existing local tests or reproduce the reported testing, and consider the work done when row-wise mode functionality is implemented and the tests pass; the issue says the code is already complete and a PR is pending approval.

Written by the indexing model from the issue text.