Stream FS2: add cache metrics

[chuwy]

In many IO-heavy enrichments we use cache (LRU mostly):

• Weather enrichment
• Currency conversion
• IP Lookups
• API Request
• SQL Query
• ~Referer parser enrichment~ (loads everything into memory straight away, as well as UA parser)

I'm wondering how many cache misses do we usually have, how much the caches used in general. Knowing that we can decide if we should execute those enrichments on separate thread pool (if still IO-heavy - separate blocking thread pool, if cache used up to 99% - main fixed thread pool).

[chuwy]

https://guava.dev/releases/22.0/api/docs/com/google/common/cache/CacheStats.html might be useful, given that scala-lru-map is a thin facade over Guava now.