Add operators for monitoring Harp device synchronization status

[glopesdev]

Online monitoring of Harp device synchronization status is an important quality control test to ensure all data is correctly timestamped. This PR adds two new operators to make it easier to compute statistics for all hardware synchronized devices.

Specifically:

HeartbeatMonitor: lifts the sequence of heartbeats of a device into a named group. Each hardware synchronized device should be placed under a HeartbeatMonitor and all the sequences merged and passed into SynchronizerMonitor.

SynchronizerMonitor: receives the sequence of named device heartbeats and computes synchronization statistics aligned on the main synchronizer heartbeat.

• MeanTimestamp: the mean timestamp value in seconds, computed from each connected Harp device
• MeanUtcTimestamp: the epoch adjusted mean timestamp value, in UTC
• ExpectedDeviceCount: the expected number of devices that should be reporting timestamps
• DeviceCount: the actual number of devices that reported a timestamp in the heartbeat window
• MaxDifference: the maximum timestamp difference, in seconds, between device timestamps
• Elements: the names of the devices which reported timestamps in the heartbeat window