Persist OringDurationTracker on partial bucket

Perist OringDurationTracker on partial buckets when the metric has
anomaly trackers. note that this isn't a perfect solution because a
config update also involves a partial bucket split, and can add new
anomaly trackers that didn't exist. However, this case is rare enough
that the slight quality tradeoff is ok.

Test: atest statsd_test
Bug: 180992558
Change-Id: Ia8bdefde5ae1fc4d7beb3d0ed63f62795fc32571
7 files changed