fix(ns-api): wireguard optimize list

[gsanchietti]

Speedup the tunnel list of ~ 190x

For a list of 100 tunnel peers:

• original time ~17 seconds
• current times ~0.85 seconds

See https://community.nethserver.org/t/wireguard-small-details/26885?u=giacomo

[Copilot]

Pull request overview

This PR optimizes WireGuard server and peer listing in ns.wireguard by reducing redundant configuration lookups and expensive subprocess calls, significantly improving listing performance at scale.

Changes:

• list_servers now reuses a single EUci instance and a pre-fetched __active_peers() snapshot across all servers.
• Refactored peer configuration generation into __generate_peer_config that accepts pre-computed server data, avoiding repeated wg pubkey and UCI lookups per peer.
• Introduced __get_server_configuration to build server objects and their peers in one pass using utils.get_all_by_type, replacing the previous O(n²)-like pattern over UCI sections.

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