Thanks for this great package!

I'm a bit confused about MongoDB implementation. It is stated in the README that an adapter can support either SlidingTimeWindow or TumblingTimeWindow, however this is not the case for MongoDB adapter as far as I can tell from the implemented interfaces.

I believe MongoDB adapter does not support SlidingTimeWindow the same way Redis Adapter does. It rather resets the stats every whole time window (more like TumblingTimeWindow but without comparing to the previous window). I came to this conclusion after checking the adapter data model and the Rate strategy and I was wondering if that is by design or a bug?