STY/WIP: check for private imports/lookups
Mostly this is an amalgam of #33479, #33394, and #33393.
looks good. We're down to 4 things that need to either be renamed or add to the ignore list: _GroupBy, _Rolling, _Rolling_and_Expanding, _IntegerDtype.

@mroeschke any preferences for the Rolling names? No preference for those. green, booyah very nice! (hopefully recent merges don't break on this :->) > hopefully recent merges don't break on this

`make check` passes on master