On very busy machines the hardwired scheduling of the ping batches could move
around among the arriving pongs, causing baseline deviations. We now wait for
each batch to complete before triggering the next one.
The broker serializer leverages the existing data_to_val() function.
During unserialization, if the destination type is any, the logic
simply wraps the broker::data value into a Broker::Data record.
Therefore, events with any parameters are currently exposed to
the Broker::Data type.
There is a bigger issue in that re-publishing such Broker::Data
instances would encode them as a normal record. Explicitly prevent
this by serializing the contained data value directly instead, similar
to what Broker already did when publishing a record.
