Flags can be used to control how features are added to the sink.
For now, there's only a single flag available - FastInsert.
When FastInsert is set, faster inserts will be use at the cost
of updating the passed features to reflect changes made at the
provider.
This includes skipping the update of the passed feature IDs
to match the resulting feature IDs for the feature within
the data provider.
Individual sink subclasses may or may not choose to respect
this flag, depending on whether or not skipping this update
represents a significant speed boost for the operation.
QgsVectorLayer always ignores the flag - feature ids are
required for the featureAdded signal to be correctly emitted,
and it's expected that performance critical applications will
add features directly to a data provider instead of
via QgsVectorLayer's edit buffer.
A simple feature sink which proxies feature addition on to another feature sink.
This class is designed to allow factory methods which always return new QgsFeatureSink
objects. Since it is not always possible to create an entirely new QgsFeatureSink
(e.g. if the feature sink is a layer or a layer's data provider), a new
QgsProxyFeatureSink can instead be returned which forwards features on to
the destination sink. The proxy sink can be safely deleted without affecting
the destination sink.
