Add clash persistence support

adapter/experimental.go

@@ -10,10 +10,17 @@ import (
 type ClashServer interface {
 	Service
 	Mode() string
+	StoreSelected() bool
+	CacheFile() ClashCacheFile
 	RoutedConnection(ctx context.Context, conn net.Conn, metadata InboundContext, matchedRule Rule) (net.Conn, Tracker)
 	RoutedPacketConnection(ctx context.Context, conn N.PacketConn, metadata InboundContext, matchedRule Rule) (N.PacketConn, Tracker)
 }
 
+type ClashCacheFile interface {
+	LoadSelected(group string) string
+	StoreSelected(group string, selected string) error
+}
+
 type Tracker interface {
 	Leave()
 }