added error handling for JSON duplicate IDs

[nwlandry]

If we construct a hypergraph as

>>> import xgi
>>> H = xgi.Hypergraph()
>>> H.add_nodes_from(["2", 2])
>>> xgi.write_json(H, "test.json")

>>> H2 = xgi.read_json("test.json")
>>> H2.nodes
NodeView(("2"))

These will get mapped to a single node when we cast IDs to strings for the JSON. This will raise an error instead.

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Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.35%. Comparing base (9140f10) to head (d7ff176).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #538      +/-   ##
==========================================
+ Coverage   92.29%   92.35%   +0.05%     
==========================================
  Files          60       60              
  Lines        4493     4500       +7     
==========================================
+ Hits         4147     4156       +9     
+ Misses        346      344       -2     

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[thomasrobiglio]

Thank you @nwlandry, looks good!

[nwlandry]

Thanks so much, @thomasrobiglio!!