Fix bug where setTimeout lingered on abort and a nested state machine was running

[nibble-4bits]

Take the following example:

const machineDefinition = {
  StartAt: "FirstState",
  States: {
    FirstState: {
      Type: "Parallel",
      Branches: [
        {
          StartAt: "Wait",
          States: {
            Wait: { Type: "Wait", Seconds: 60, End: true },
          },
        },
      ],
      End: true,
    },
  },
};

const stateMachine = new StateMachine(machineDefinition);
const { abort } = stateMachine.run(input);

abort();

When calling abort() after starting the execution, the execution is aborted, however, the script doesn't completely finish as the sleep call from the inner Wait state isn't canceled. In this example, that means the setTimeout in sleep won't resolve until the 60 seconds specified in Seconds have elapsed.

This PR fixes that behavior.