Rename file and class in magic subtree

[ulemanstreaming]

Since we're covering the API of the Analytics Engine, it makes sense to call the callable module and class analytics_engine_client.py and AnalyticsEngineClient. But for the magic equivalent, analytics_magic_client.py and AnalyticsMagicClient lose the fact that it's the Analytics Engine we're talking about, not some general Analytics.

I propose that we rename file and class to analytics_engine_magic.py and AnalyticsEngineMagic, respectively.