@Override
    public Map<TensorAddress, Double> cells() {
        ImmutableMap.Builder<TensorAddress, Double> builder = new ImmutableMap.Builder<>();
        var iter = cellIterator();
        while (iter.hasNext()) {
            Cell cell = iter.next();
            builder.put(cell.getKey(), cell.getValue());
        }
        return builder.build();
    }
Returns an iterator over the values of this tensor.
The iteration order is the same as for cellIterator.
vespajlib/src/main/java/com/yahoo/tensor/MixedTensor.java