Track retrieval successes and failures

Retrieval types to track
* [x] Bitswap
* [x] HTTP
* [ ] Graphsync

Metrics to Track:
* Successes
* Failures where not found
* Other failures

Start by locating the Bitswap and HTTP retrieval paths and checking for existing metrics instrumentation. Investigate where Graphsync retrieval is handled, then verify that each listed retrieval type reports successes, not-found failures, and other failures.

Written by the indexing model from the issue text.