This PR removes the last production usage for: `LastArchivedRoot` by
- extend the P2P config to accept a `StateGen` dependency and wire it up
from the beacon node
- update gossip scoring to read the active validator count via stategen
using last finalized block root
note: i think the correct implementation should process last finalizes
state to current slot, but that's a bigger change i dont want to make in
this PR, i just want to remove usages for `LastArchivedRoot`
