class GetNext

Returns a vector of [fuchsia.diagnostics/FormattedContent] structs

with a format dictated by the format_settings argument provided to the Reader protocol

which spawned this BatchIterator.

An empty vector implies that the data hierarchy has been fully iterated, and subsequent

GetNext calls will always return the empty vector.

When the BatchIterator is serving results via subscription model, calls to GetNext will

hang until there is new data available, it will not return an empty vector.

- returns a vector of FormattedContent structs. Clients connected to a

Batch are expected to call GetNext() until an empty vector

is returned, denoting that the entire data hierarchy has been read.

* error a [fuchsia.diagnostics/ReaderError]

value indicating that there was an issue reading the underlying data hierarchies

or formatting those hierarchies to populate the `batch`. Note, these

issues do not include a single component's data hierarchy failing to be read.

The iterator is tolerant of individual component data sources failing to be read,

whether that failure is a timeout or a malformed binary file.

In the event that a GetNext call fails, that subset of the data hierarchy results is

dropped, but future calls to GetNext will provide new subsets of

FormattedDataHierarchies.