Add performance metrics for experiments

What does this MR do?

This adds metrics to track experiment performance. This is mostly so we can make sure that when we take steps to improve performance, we can get an idea of how we're improving performance. Tracking performance is the first step to improving performance.

This is just a first pass, and we should consider adding more details to this as we continue to iterate on experimentation.

This implementation is about the benchmark of the behavior block that's defined within the experiment itself and doesn't account for the time taken in resolving and assigning the variant. This variant resolution logic plays a notable role in the overall performance of an experiment -- since it has to fall back to using Flipper Gates for certain aspects, so we should prioritize adding some performance metrics around that as well.

Conformity

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