Counter-type metrics for samplers are broken

[kentquirk]

Versions

• Refinery: all recent

Steps to reproduce

1. Use an EMADynamic sampler (or anything that has an AdjustmentInterval)
2. Send its metrics to Honeycomb
3. Note that the metric count seems to increase exponentially

The problem is that Refinery is reading a counter and wanting to increment the metrics counter to get the same result -- but never records the previous value, so is just always incrementing by the value of the counter.

This is a bug in several sampler implementations. Can we centralize the code to a helper function?

Additional context
Pollinators thread