refactor(p2p): move node name registry into P2PServer

[conache]

🗒️ Description / Motivation

The PeerId -> node_name lookup lived in a global RwLock<HashMap<PeerId, &'static str>> populated once at startup. This PR moves it into P2PServer so the actor owns its own state.

What Changed

• crates/net/p2p/src/lib.rs: the registry is now a field on the P2P actor's state struct, with a small helper to resolve a peer's name.
• crates/net/p2p/src/metrics.rs: no longer owns the registry — its peer-event helpers take the resolved name directly.
• bin/ethlambda/src/main.rs: the loader now returns the map and hands it off to P2P::spawn at startup; it also logs how many entries it loaded.

Correctness / Behavior Guarantees

• Metric label values (lean_connected_peers{client="..."}) are unchanged for valid configs.
• Bad rows in validator-config.yaml (unparseable secp256k1 privkeys) used to be silently dropped; they now emit a warn! per drop and are still skipped. No new panics, no new failure paths.
• No consensus-layer impact (fork choice, attestations, STF, signatures untouched).

Tests Added / Run

• make fmt
• make lint
• make test

Related Issues / PRs

• Closes Move node name registry to each module #106