Output ratios should be computed over the whole metric window instead of averaged

Currently Output ratios are computed during metric collection based on the current in/out metrics an stored as part of the collected metrics.

During evaluation the output ratios previously computed are then averaged together in the metric window. This however leads to incorrect computation due to the nature of the computation and averaging.

Example:
Let's look at a window operator that simply sorts and re-emits events in windows. During the window collection phase, output ratio will be computed and stored as 0. During the window computation the output ratio will be last_input_rate / window_size.  Depending on the last input rate observation this can be off when averaged into any direction.