Don't use AnnounceHandler by value

It needs to share mutex for upstream tracker single flight handling.

tracker/http/server/server.go

@@ -18,7 +18,7 @@ import (
 )
 
 type Handler struct {
-	Announce tracker.AnnounceHandler
+	Announce *tracker.AnnounceHandler
 	// Called to derive an announcer's IP if non-nil. If not specified, the Request.RemoteAddr is
 	// used. Necessary for instances running behind reverse proxies for example.
 	RequestHost func(r *http.Request) (netip.Addr, error)

tracker/udp/server/server.go

@@ -32,7 +32,7 @@ type AnnounceTracker = tracker.AnnounceTracker
 type Server struct {
 	ConnTracker  ConnectionTracker
 	SendResponse func(data []byte, addr net.Addr) (int, error)
-	Announce     tracker.AnnounceHandler
+	Announce     *tracker.AnnounceHandler
 }
 
 type RequestSourceAddr = net.Addr