client/visitor: deduplicate visitor connection handshake and wrapping

Extract two shared helpers to eliminate duplicated code across STCP,
SUDP, and XTCP visitors:

- dialRawVisitorConn: handles ConnectServer + NewVisitorConn handshake
  (auth, sign key, 10s read deadline, error check)
- wrapVisitorConn: handles encryption + pooled compression wrapping,
  returning a recycleFn for pool resource cleanup

SUDP is upgraded from WithCompression to WithCompressionFromPool,
aligning with the pooled compression used by STCP and XTCP.

pkg/metrics/mem/server.go

@@ -143,6 +143,7 @@ func (m *serverMetrics) OpenConnection(name string, _ string) {
 	proxyStats, ok := m.info.ProxyStatistics[name]
 	if ok {
 		proxyStats.CurConns.Inc(1)
+		m.info.ProxyStatistics[name] = proxyStats
 	}
 }
 
@@ -154,6 +155,7 @@ func (m *serverMetrics) CloseConnection(name string, _ string) {
 	proxyStats, ok := m.info.ProxyStatistics[name]
 	if ok {
 		proxyStats.CurConns.Dec(1)
+		m.info.ProxyStatistics[name] = proxyStats
 	}
 }
 
@@ -166,6 +168,7 @@ func (m *serverMetrics) AddTrafficIn(name string, _ string, trafficBytes int64)
 	proxyStats, ok := m.info.ProxyStatistics[name]
 	if ok {
 		proxyStats.TrafficIn.Inc(trafficBytes)
+		m.info.ProxyStatistics[name] = proxyStats
 	}
 }
 
@@ -178,6 +181,7 @@ func (m *serverMetrics) AddTrafficOut(name string, _ string, trafficBytes int64)
 	proxyStats, ok := m.info.ProxyStatistics[name]
 	if ok {
 		proxyStats.TrafficOut.Inc(trafficBytes)
+		m.info.ProxyStatistics[name] = proxyStats
 	}
 }
 
@@ -236,9 +240,15 @@ func (m *serverMetrics) GetProxiesByTypeAndName(proxyType string, proxyName stri
 	m.mu.Lock()
 	defer m.mu.Unlock()
 
-	proxyStats, ok := m.info.ProxyStatistics[proxyName]
-	if ok && proxyStats.ProxyType == proxyType {
-		res = toProxyStats(proxyName, proxyStats)
+	for name, proxyStats := range m.info.ProxyStatistics {
+		if proxyStats.ProxyType != proxyType {
+			continue
+		}
+		if name != proxyName {
+			continue
+		}
+		res = toProxyStats(name, proxyStats)
+		break
 	}
 	return
 }