handle of a queried stream. (must have ownership)
called when a row is fetched, contains either an error that can be accessed within the callback or a row handle that can be moved out the callback, but must be freed with rorm_row_free.
context pointer to pass through as-is into the callback.
This function is running in an asynchronous context.
Fetches the next row from the stream. Must not be called in parallel on the same stream. Returns Error.NoRowsLeftInStream when the stream is finished.