fix: enable metrics before loading services

Move xmetrics.Enable(true) from run() to Start(), before loader.Load(),
so that listener wrappers can observe the enabled state at Init time
rather than after wrapper decisions have already been made.

cmd/gost/program.go

@@ -62,6 +62,12 @@ func (p *program) Start() error {
 
 	config.Set(cfg)
 
+	// Enable metrics before loading services so that listener wrappers
+	// can observe the enabled state at Init time.
+	if cfg.Metrics != nil && cfg.Metrics.Addr != "" {
+		xmetrics.Enable(true)
+	}
+
 	if err := loader.Load(cfg); err != nil {
 		return err
 	}
@@ -121,8 +127,6 @@ func (p *program) run(cfg *config.Config) error {
 
 		p.srvMetrics = s
 
-		xmetrics.Enable(true)
-
 		go func() {
 			defer s.Close()