Atomic: Refactor

The Atomic package needs some refactoring as noted in #2088:

* [ ] The `query_object` method should be removed in favor of using an `_async` method with the default wrapper
* [ ] The keyword arguments should be changed to `**kwargs` when they have a `None` default (or... maybe we should just be adding a `*` in front of all those keyword args? @bsipocz chime in here to clarify what you meant in https://github.com/astropy/astroquery/pull/2088#discussion_r655623808)

Start by reading the Atomic package and the refactoring notes in issue #2088, including the linked pull-request discussion for the unresolved keyword-argument choice. Locate query_object and the methods with None defaults, then confirm the checklist requirements and relevant existing tests before considering the work done.

Written by the indexing model from the issue text.