Require substantially more samples before a peer's request-latency EMA
becomes eligible for protection. A 10-sample floor was too low: a peer
hitting 10 fast replies in a short burst could earn protection before
the slow alpha=0.01 EMA had moved meaningfully away from the bootstrap
value. At ~70-sample EMA half-life, a 100-sample floor means the EMA
has been refined through several half-lives before it can affect
dropping decisions.
Updates the dropper tests that previously used RequestSamples=50 to
use peerstats.MinLatencySamples so they stay robust to future value
changes. Design notes and a test comment reference the new value.
Introduces a new eth/peerstats package as the single home for per-peer
quality metrics consumed by the dropper. txtracker shrinks to a pure
tx-lifecycle role: it maps tx hash to deliverer, subscribes to chain
heads, computes per-block per-peer inclusion and finalization deltas,
and emits them to a StatsConsumer.
peerstats owns the aggregates: inclusion EMA, finalized counter,
latency EMA, sample counter, and the MinLatencySamples bootstrap
constant the dropper uses to filter under-sampled peers. It's a
plain struct with a mutex — no goroutine of its own, no lifecycle
management. The fetcher's onRequestLatency callback now flows to
peerStats.NotifyRequestLatency, the handler's unregisterPeer cleans
up via peerStats.NotifyPeerDrop, and the dropper reads its snapshot
via peerStats.GetAllPeerStats.
txtracker.handleChainHead computes deltas under its own lock, then
releases the lock before calling the consumer, which avoids any
cross-package lock ordering. Tests are split along the same line:
tracker tests use a mock consumer to assert what signals are emitted,
peerstats tests cover EMA math and aggregation semantics directly.
