CoW: Track references in unstack if there is no copy
- [ ] xref #56633
- [ ] All [code checks passed](https://pandas.pydata.org/pandas-docs/dev/development/contributing_codebase.html#pre-commit).
- [ ] Added an entry in the latest `doc/source/whatsnew/vX.X.X.rst` file if fixing a bug or adding a new feature.

cc @jorisvandenbossche @rhshadrach 

@rhshadrach was correct, we can get there without making a copy. it's a special case, but nevertheless

might be worth back porting, but not necessary this one should be good to merge Thanks @phofl 