feat(node): Clean old P2P stack

[KaffinPX]

No description provided.

[milltay]

Reviewed and merged. This matches the removal map end-to-end: the three shared symbols were relocated before the delete (network/codec.rs + close_peer_connected_callback into peer_loop.rs), legacy transport is fully gone (listener, call_peer/answer_peer, magic strings, port-9798 routing, PotentialPeers discovery), HandshakeData.listen_port removed, discovery messages dropped, IP standing now derived directly from the Multiaddr, and the StickyPeers stuck-on-Dialing fix is a nice catch. Verified with a full-workspace cargo check on the merge result against current main (branch was based pre-#3; no conflicts, #3's rpc changes intact).

Follow-ups worth a look, none blocking:

1. HandshakeData's bincode layout changed but the substream protocol id is still /id/stream-gateway-handshake/1.0 — old↔new nodes will fail with a decode error instead of a clean mismatch. Fine for a coordinated testnet flip; consider bumping to /1.1 as hygiene.
2. Three CLI flags are now definition-only no-ops: --max-connections-per-ip, --reconnect-cooldown, --handshake-timeout (--restrict-peers-to-list still works via the discovery gate). Either drop them or wire them into the actor's should_bounce.
3. Pre-existing gaps that matter more now that libp2p is the only stack: spawn_peer_loop passes rand::random_bool(0.5) as the inbound flag (actor.rs:2181 — endpoint.is_dialer() has the truth), and the Main bootstrap seed is still 127.0.0.1:9899 (address_book.rs:315).
4. MainLoopHandler::now() is newly dead code (its callers went with the legacy machinery).