The NativeAdsManager provides a mechanism to fetch a set of NativeAds and then use them within
your application. The recommended usage is to call nextNativeAd() at the moment when you are
about to render an ad. The NativeAdsManager can hold at most 10 unique ads at once but supports
giving out as many ads as needed by cloning over the set of NativeAds it got back from the server
which can be useful for feed scenarios.
When calling loadAds() an optional NativeAd.MediaCacheFlag can be passed to indicate whether to
pre-cache the ad images (image, icon, all, or none). If not set, no images will be pre-cached
before onAdsLoaded() is called.