[PECO-1263] Separate get_status and poll_for_status methods

[susodapop]

Description

Per guidance from @benc-db, I've separated the get_result_or_status method into separate calls. The hello world for this interface now looks like this:

        with self.connection() as conn:
            ae = conn.execute_async("select :param `col`", {"param": 1})
            while ae.is_running:
                ae.poll_for_status()
                time.sleep(1)

What's next?

I need to teach AsyncExecution how to pick up a running execution that was started by another thread.

[susodapop]

This is just an alias. Should I just rename the _thrift_get_operation_status method?

[benc-db]

My instinct is yes, just rename the other method. The more nuanced answer is, it depends on if you think the private version of the method will evolve in ways that the public version could be refactored to adapt for without changing the interface. The benefit of a private method is that you should feel comfortable changing private interfaces without breaking consumers...however python doesn't really enforce private, so the waters get muddied. So yeah, I say just rename the existing method.

[susodapop]

This was a black reformat unrelated to this PR.

[susodapop]

For simplicity I added this pytest fixture so I don't need to duplicate this code for my "raises an exception" assertions.