TUN-8775: Make sure the session Close can only be called once

The previous capture of the sync.OnceValue was re-initialized for each
call to `Close`. This needed to be initialized during the creation of
the session to ensure that the sync.OnceValue reference was held for
the session's lifetime.

Closes TUN-8775

quic/v3/session_test.go

@@ -255,11 +255,16 @@ func TestSessionClose_Multiple(t *testing.T) {
 	if !origin.closed.Load() {
 		t.Fatal("origin wasn't closed")
 	}
+	// Reset the closed status to make sure it isn't closed again
+	origin.closed.Store(false)
 	// subsequent closes shouldn't call close again or cause any errors
 	err = session.Close()
 	if err != nil {
 		t.Fatal(err)
 	}
+	if origin.closed.Load() {
+		t.Fatal("origin was incorrectly closed twice")
+	}
 }
 
 func TestSessionServe_IdleTimeout(t *testing.T) {