Consider adding a hearbeat check to the workflow

We were waiting for https://github.com/harp-tech/core.pico/issues/65 to be implemented; however, recent sessions have highlighted the importance of an interim solution that we should consider.

The low-hanging fruit would be to simply check for a heartbeat without checking for synchronism, as the "Seconds" register heartbeat is backwards-compatible and enabled in the current version of the workflow.
Note that this solution would NOT ensure synchronism across all devices in the harp hub as this feature is only implemented in the latest spec.