Add normalized Moran's I statistic and tests

[diegogiuliani-unitn]

This PR adds the normalized Moran's I index and its inferential procedure under normality, based on our forthcoming paper in International Statistical Review, "Revisiting the Normalization of the Moran's I Index: A Correlation-based Approach with Inference".

Changes included:
Added implementation functions to R/
Added manual documentation in man/
Updated NAMESPACE exports and NEWS
Added unit tests in tests/

We have ensured our implementation aligns with spdep's standard formula conventions and spatial weights handling.

[rsbivand]

@diegogiuliani-unitn Do you have a DOI for your article? It would be very helpful to link to it directly in that way.

[diegogiuliani-unitn]

@rsbivand Yes. It is this one: https://doi.org/10.1111/insr.70067, but it is not active yet. Should I add it anyway?

[rsbivand]

@diegogiuliani-unitn Do you know when it will be active?

[diegogiuliani-unitn]

@rsbivand I don't, I am sorry. But it should be soon.

[rsbivand]

@diegogiuliani-unitn please remove testthat from DESCRIPTION and only use tinytest - I see you are using it anyway. Also remove the Rproj file, and any debris that may have brought with it.

[diegogiuliani-unitn]

@rsbivand I did it. My apologies, but I am new to this kind of thing.

[rsbivand]

@diegogiuliani-unitn not a problem! The Rstudio things work best for single developer or single-team settings, where Rproj shares common settings. This isn't the case here, as contributors use various tools. I'll carry on looking at the code, but it may take some time. Do you need rapid inclusion for your article?

[diegogiuliani-unitn]

@rsbivand Do not worry! Whenever you have time, thanks. If the paper's publication concludes before the package addition is ready, can we note somewhere in the paper that the functions to implement the index will be included in "spdep" in the near future?

[rsbivand]

@diegogiuliani-unitn Yes, that would be fine. There are a few other things to do before a submission to CRAN that I need to make progress on.

[diegogiuliani-unitn]

@rsbivand Great! Many thanks