Draft: feat: implement box_effective_su for C API
box_effective_su() allows to change only effective user, while the session user does not change.
NO_DOC=picodata internal patch NO_CHANGELOG=picodata internal patch NO_TEST=picodata internal patch
box_effective_su() allows to change only effective user, while the session user does not change.
NO_DOC=picodata internal patch NO_CHANGELOG=picodata internal patch NO_TEST=picodata internal patch