fix(cli): release runtime resources across startup and shutdown

Co-authored-by: Ginder Singh <ginder@windscribe.com>

cmd/cli/network_monitor_test.go

@@ -13,6 +13,8 @@ type sourceTestMonitor struct {
 	started  bool
 }
 
+func (*sourceTestMonitor) Close() error { return nil }
+
 func (m *sourceTestMonitor) RegisterChangeCallback(fn netmon.ChangeFunc) func() {
 	m.callback = fn
 	return func() {}