We improved performance on the List Email Activity endpoint.

We realized we were fetching bounce activity from an inefficient source. With a more efficient method to fetch this information, this endpoint is now running an order of magnitude faster — the average request time has gone from 6 seconds to 200 milliseconds. 

This change also makes this endpoint more consistent with bounce activity displayed in the web application. Previously, if an email server returned multiple bounces for a single recipient in a given campaign, this endpoint would include the latest one, whereas the web application would show the first one. As of this change, this endpoint will respond with the first bounce.