Change the long-term protection category from total inclusions to
total finalized inclusions. Finalized txs are harder to game (require
actual block finality, not just inclusion) and represent confirmed
on-chain value.
The recent-inclusion EMA stays on chain head inclusions for
responsiveness — a peer delivering txs that appear in the latest
blocks gets quick protection without waiting for finalization.
The tracker now checks CurrentFinalBlock() on each chain head event
and credits delivering peers for all newly finalized blocks since
the last check.
Minimal txtracker that records which peer delivered each transaction
and credits peers when their transactions appear on chain. Provides
the PeerInclusionStats needed by the dropper's protection logic.
Design:
- NotifyReceived(peer, txs): records deliverer per tx hash (called
from handler_eth.go when tx bodies arrive via P2P)
- Subscribes to ChainHeadEvent, fetches block txs, credits the
delivering peer for each included tx
- Per-peer EMA of recent inclusions (alpha=0.05), updated every block
- LRU eviction at 262K entries to bound memory
- Mutex-based (not channel-based) for simplicity — the hot path
(NotifyReceived) is a fast map insert
Wired into the dropper via an adapter callback in backend.go that
converts txtracker.PeerStats to the dropper's PeerInclusionStats.
