feat(net): expose per-kind reputation-change and ban counters

[constwz]

Summary

Adds per-`ReputationChangeKind` and per-outcome counters to the network's `PeersManager`, so reputation-driven peer drops are visible at the Prometheus layer.

Why

Today, a peer-pool drain induced by reputation bans is invisible at the metrics layer:

• Banned peers go into the `ban_list`, which has no exposed gauge or counter.
• The existing `DisconnectMetrics` counters cannot tell a graceful close apart from a rep-driven kick — both increment `network_disconnect_requested`.
• `apply_reputation_change` only emits a `debug`/`info` log line per call (since fix: resolve some issues in cross region test #175), which is fine for forensics but useless for Grafana.

Concretely this affects BSC node operators investigating the peers drop to zero after sync pattern (bnb-chain/reth-bsc#320). Without these counters, distinguishing "we are banning peers because of repeated `BadBlock` penalties" from "peers are leaving us for unrelated reasons" requires log inspection. With them, a single PromQL `rate(network_reputation_changes_bad_block[5m])` correlated against `network_connected_peers` makes the diagnosis a panel.

New metrics

```
network_reputation_changes_bad_message
network_reputation_changes_bad_block
network_reputation_changes_bad_transactions
network_reputation_changes_bad_announcement
network_reputation_changes_already_seen_transaction
network_reputation_changes_timeout
network_reputation_changes_bad_protocol
network_reputation_changes_failed_to_connect
network_reputation_changes_dropped
network_reputation_changes_reset
network_reputation_changes_other
network_bans_total
network_disconnect_and_bans_total
network_unbans_total
```

Behaviour

• The kind-counter increments before the trusted-peer / unknown-peer guards — it answers "what's hitting us." Outcome counters answer "did we punish for it."
• Trusted-peer exemption is preserved.
• No behaviour change beyond the new counters.

Test plan

• `cargo check -p reth-network` — pass
• `cargo +nightly clippy -p reth-network --tests --all-features` — no new warnings
• `cargo +nightly fmt --check` — clean
• `cargo nextest run -p reth-network` — 177 passed, 4 skipped

Refs bnb-chain/reth-bsc#320.