Use specific metrics/counters for the reducers

[BeJF]

Ideally, we should promote metrics / counters rather than logs for these high-frequency observations (as when data as been added to the Storage). Might be a nice addition for a follow up (from the utxo_by_address filter PR).

Originally posted by @scarmuega in https://github.com/txpipe/scrolls/pull/18#discussion_r887244518