hbbs: enforce outbound initiator whitelist by peer ID

[tango103]

Motivation

• Add server-side enforcement so only authorized peer IDs can initiate outbound (A->B) punch-hole/relay requests while keeping inbound receive behavior unchanged.
• Provide a simple, file-based whitelist (whitelist.txt) that is easy to edit on the server and only affects hbbs logic.

Description

• Load whitelist.txt at hbbs startup (one ID per line, ignore empty lines and lines beginning with #) and store it in RendezvousServer::outbound_whitelist via load_outbound_whitelist.
• Before forwarding a PunchHoleRequest in handle_punch_hole_request, resolve the source peer ID from the request SocketAddr using a new helper PeerMap::get_id_by_socket_addr and reject the request if the source ID is missing or not in the whitelist.
• Added PeerMap::get_id_by_socket_addr to map a SocketAddr to the peer ID by scanning the in-memory PeerMap.
• Added a template whitelist.txt and updated src/rendezvous_server.rs and src/peer.rs to implement the feature.

Testing

• Ran rustfmt on the modified files with rustfmt --edition 2021 src/rendezvous_server.rs src/peer.rs which completed successfully.
• Attempted cargo fmt --all which failed in this environment because the workspace member libs/hbb_common is missing, so full workspace formatting could not be performed.
• Attempted cargo check -p hbbs which failed for the same reason (libs/hbb_common/Cargo.toml missing), so a full build/check could not be completed here.

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Codex Task