[DF] Also test jitted/compiled reading of nested columns
[DF] Also test jitted/compiled reading of nested columns

This is a regression test: jitted reading with this kind of branches
broke due to a change in TTree logic (see ROOT-10942): we can read
them as `"leafname"` but not as `"branchname.leafname"`, and
`rdf.GetColumnNames()` now returns both spellings.

olifre/root,root-mirror/root,karies/root,olifre/root,root-mirror/root,root-mirror/root,karies/root,karies/root,karies/root,olifre/root,root-mirror/root,karies/root,root-mirror/root,olifre/root,olifre/root,olifre/root,karies/root,karies/root,olifre/root,karies/root,root-mirror/root,karies/root,olifre/root,root-mirror/root,root-mirror/root,olifre/root,karies/root,olifre/root,root-mirror/root,root-mirror/root,karies/root,olifre/root,root-mirror/root