Feature request - be able to tell if API was resolved by memory, cache, or source

I would like to be able to tell what resolved an API call. This can currently be resolved by either the in-memory cache, and external cache, or the actual source. This is needed for a billing log I am needing to write and I accumulate the data as the request is being processed (in my datasource code). This could be a feature that is 'turned on' somehow, so that users that do not need the feature will not enable it.

Start by tracing the datasource code where API requests are resolved and where request data is accumulated for billing. Determine how in-memory cache, external cache, and the source are distinguished, and define an opt-in way to expose that resolution. Done means callers can reliably identify the resolution source without affecting users who do not enable the feature.

Written by the indexing model from the issue text.