feat: observe HTTP2 reset and goaway frames

transport/http2/lifecycle_test.go

@@ -160,6 +160,9 @@ func TestShutdownSendsGoAwayAndDrains(t *testing.T) {
 	if err := rctx.Err(); err != nil {
 		t.Fatalf("graceful shutdown canceled active request: %v", err)
 	}
+	if stats := s.Stats(); stats.GoAwayFrames != 1 {
+		t.Fatalf("expected one observed GOAWAY frame, got %+v", stats)
+	}
 	select {
 	case err := <-done:
 		t.Fatalf("Serve returned before drain: %v", err)
@@ -214,6 +217,9 @@ func TestRSTStreamCancelsOnlyOneRequest(t *testing.T) {
 	case <-time.After(time.Second):
 		t.Fatal("RST did not cancel request")
 	}
+	if stats := s.Stats(); stats.RSTStreams != 1 {
+		t.Fatalf("expected one observed RST_STREAM, got %+v", stats)
+	}
 	release <- struct{}{}
 	if got := p.body(t, 3); got != "/survive" {
 		t.Fatalf("sibling body=%q", got)