Disable the per-second timer when we can
Once the children of #25375 (moved) are merged, there will be nothing left in second_elapsed_callback that needs to happen once per second when Tor isn't running. Once we're in that position, we can disable this callback whenever..
- we are completely hibernating (state == DORMANT) OR the network is disabled.
- The controller is not waiting for any per-second events.
This change will require some related refactoring.