Updated the return type of Katz centrality

[nwlandry]

This PR accomplishes the following:

• katz_centrality now returns a dictionary to be consistent with all other centrality measures.
• The Katz centrality is now 1-normalized consistent with other functions
• katz_centrality is now a nodestat as well.

[codecov]

Codecov Report

Attention: Patch coverage is 86.66667% with 2 lines in your changes are missing coverage. Please review.

Project coverage is 92.12%. Comparing base (369a10a) to head (eb3258b).

Files	Patch %	Lines
xgi/stats/nodestats.py	33.33%	2 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #530      +/-   ##
==========================================
- Coverage   92.19%   92.12%   -0.07%     
==========================================
  Files          60       60              
  Lines        4392     4393       +1     
==========================================
- Hits         4049     4047       -2     
- Misses        343      346       +3     

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[thomasrobiglio]

Looks good! We should mention that the values that are returned are normalised, can you add that?

[nwlandry]

Looks good! We should mention that the values that are returned are normalised, can you add that?

I have mentioned that centralities are 1-normalized in the Returns field.

[nwlandry]

Thanks for the review!!