Add v2ray stats api

constant/err.go

@@ -3,3 +3,5 @@ package constant
 import E "github.com/sagernet/sing/common/exceptions"
 
 var ErrTLSRequired = E.New("TLS required")
+
+var ErrQUICNotIncluded = E.New(`QUIC is not included in this build, rebuild with -tags with_quic`)