Add lazy P2P demand tracking and need_p2p override (#2003)

- add lazy_p2p so nodes only start background P2P for peers that actually have recent business traffic
- add need_p2p so specific peers can still request eager background P2P even when other nodes enable lazy mode
- cover the new behavior with focused connector/peer-manager tests plus three-node integration tests that verify relay-to-direct route transition

easytier/src/instance/dns_server/tests.rs

@@ -45,7 +45,7 @@ pub async fn prepare_env_with_tld_dns_zone(
         if let Some(zone) = tld_dns_zone {
             flags.tld_dns_zone = zone.to_string();
         }
-        ctx.config.set_flags(flags);
+        ctx.set_flags(flags);
     }
 
     let (s, r) = create_packet_recv_chan();