Expose ring internal functions

A number of ring internal methods are useful beyond their usage in purely ring apps (e.g. for writing a pedestal/reitit interceptor), such as [record-metrics!](https://github.com/clj-commons/iapetos/blob/master/src/iapetos/collector/ring.clj#L110). Since these are private, it's unreliable to depend on them. Thoughts on exposing these?