deduplicate common logic across proxy, visitor, and metrics modules (#5213)

- Replace duplicate parseBasicAuth with existing httppkg.ParseBasicAuth
- Extract buildDomains helper in BaseProxy for HTTP/HTTPS/TCPMux proxies
- Extract toProxyStats helper to deduplicate ProxyStats construction
- Extract startVisitorListener helper in BaseProxy for STCP/SUDP proxies
- Extract acceptLoop helper in BaseVisitor for STCP/XTCP visitors

client/visitor/xtcp.go

@@ -65,10 +65,10 @@ func (sv *XTCPVisitor) Run() (err error) {
 		if err != nil {
 			return
 		}
-		go sv.worker()
+		go sv.acceptLoop(sv.l, "xtcp local", sv.handleConn)
 	}
 
-	go sv.internalConnWorker()
+	go sv.acceptLoop(sv.internalLn, "xtcp internal", sv.handleConn)
 	go sv.processTunnelStartEvents()
 	if sv.cfg.KeepTunnelOpen {
 		sv.retryLimiter = rate.NewLimiter(rate.Every(time.Hour/time.Duration(sv.cfg.MaxRetriesAnHour)), sv.cfg.MaxRetriesAnHour)
@@ -93,30 +93,6 @@ func (sv *XTCPVisitor) Close() {
 	}
 }
 
-func (sv *XTCPVisitor) worker() {
-	xl := xlog.FromContextSafe(sv.ctx)
-	for {
-		conn, err := sv.l.Accept()
-		if err != nil {
-			xl.Warnf("xtcp local listener closed")
-			return
-		}
-		go sv.handleConn(conn)
-	}
-}
-
-func (sv *XTCPVisitor) internalConnWorker() {
-	xl := xlog.FromContextSafe(sv.ctx)
-	for {
-		conn, err := sv.internalLn.Accept()
-		if err != nil {
-			xl.Warnf("xtcp internal listener closed")
-			return
-		}
-		go sv.handleConn(conn)
-	}
-}
-
 func (sv *XTCPVisitor) processTunnelStartEvents() {
 	for {
 		select {