Refactor wireguard & add tun support

transport/wireguard/device_stack_stub.go

@@ -0,0 +1,9 @@
+//go:build no_gvisor
+
+package wireguard
+
+import "github.com/sagernet/sing-tun"
+
+func NewStackDevice(localAddresses []netip.Prefix, mtu uint32) (Device, error) {
+	return nil, tun.ErrGVisorNotIncluded
+}