Expose cache age
Currently dogpile.cache has the created time stored in metadata in the cache, inside value.metadata["ct"] but doesn't expose this anywhere.
We have some very heavy operations and even if the cache gets invalidated, we want to let it stay stale for up to 5 minutes afterwards during high traffic but we need to pull be able to decide when to regenerate the cache based on the size of the survey.
If we have a survey that has only 10 respondents, we want to invalidate the cache every time a new respondent comes in.
If a survey has 500 respondents or more, even while new respondents are filling out the survey, we would like to leave the cache in place for up to 5 minutes before we regenerate it.
I would be happy with a get_with_metadata and get_or_create_with_metadata, that way after the call I could inspect the age of the cache from metadata['ct'] and decide if I should invalidate it.