Internally, rather than using the multi-dimensional character of
tensors to compute all sites and all lead times at once, loops are
performed for each site and each lead time, in turn, in order to
minimise memory imprint. Although at the moment, the input tensors are
expected to feature the sites and lead times dimensions. If memory is
an issue, the user can still send smaller tensors with size 1 for those
dimensions and recompose multi-sites/multi-lead times output arrays
externally.