@Override
    public void encode(GrowableByteBuffer buffer, Tensor tensor) {
        if ( ! ( tensor instanceof IndexedTensor))
            throw new RuntimeException("The dense format is only supported for indexed tensors");
        encodeDimensions(buffer, (IndexedTensor)tensor);
        encodeCells(buffer, (IndexedTensor)tensor);
    }
Implementation of a dense binary format for a tensor on the form:

Sorted dimensions = num_dimensions [dimension_str_len dimension_str_bytes dimension_size_int]*
Cell_values = [double, double, double, ...]*
where values are encoded in order of increasing indexes in each dimension, increasing
indexes of later dimensions in the dimension type before earlier.

@author bratseth
vespajlib/src/main/java/com/yahoo/tensor/serialization/DenseBinaryFormat.java