Extract reusable parts to a shared library

RoundCounter is a useful wrapper on top of prometheus to round metrics to 8. We want to use it in other projects like rdsys.

Another useful piece for other projects is safelog that is already being imported by bridgestrap and conjure. Maybe we want to be able to import it without snowflake.

We could bundle both into a single library as this might make it easier to add other pieces in the future and each extra library makes it harder to package software to distros.