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/proto/api_manage.proto

@@ -85,6 +85,8 @@ message NetworkConfig {
   common.SecureModeConfig secure_mode = 55;
   reserved 56;
   optional string credential_file = 57;
+  optional bool lazy_p2p = 58;
+  optional bool need_p2p = 59;
 }
 
 message PortForwardConfig {

easytier/src/proto/common.proto

@@ -70,6 +70,9 @@ message FlagsInConfig {
   bool p2p_only = 32;
 
   bool disable_tcp_hole_punching = 34;
+
+  bool lazy_p2p = 37;
+  bool need_p2p = 38;
 }
 
 message RpcDescriptor {
@@ -217,6 +220,7 @@ message PeerFeatureFlag {
   bool quic_input = 6;
   bool no_relay_quic = 7;
   bool is_credential_peer = 8;
+  bool need_p2p = 9;
 }
 
 enum SocketType {