refactor: File.handle_is_private_changed
refactor: File.handle_is_private_changed

* Make file renaming atomic
* Add rollback observer to maintain filesystem consistency
* Simplify logic

StrellaGroup/frappe,frappe/frappe,frappe/frappe,yashodhank/frappe,StrellaGroup/frappe,frappe/frappe,yashodhank/frappe,StrellaGroup/frappe,yashodhank/frappe,yashodhank/frappe