Reduce unnecessary sleep after API calls

[mesozoic]

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Right now ApiAbstract._iterate calls time.sleep before yielding the results of its first API call. This slows down operations that only retrieve a single record (or a single page of results) and it seems unnecessary unless we're about to request a second page of results.

This moves the time.sleep call to the end of the loop, so it only happens if we need to fetch a second page.