address review comments
* rename `group_factory` to `group_cls` in `make_group_from_vertices` * use `bit_length` to avoid floating point fuzz * add `_acf` to meshmode for easier test running
* rename `group_factory` to `group_cls` in `make_group_from_vertices` * use `bit_length` to avoid floating point fuzz * add `_acf` to meshmode for easier test running