Add the NAryRelation class

[johnHostetter]

The NAryRelation class is used to represent n-ary fuzzy relations, such as t-norms or t-conorms. It allows a convenient and consistent interface to working with fuzzy compound propositions for fuzzy logic, allows the end-user to determine how missing information should be handled, and how to calculate these compound truth values. It also provides the Compound class, allowing multiple different implementations of NAryRelation to coincide and be aggregated together for subsequent operations. Lastly, the NAryRelation implements how a n-ary fuzzy relation should be represented as a directed igraph.Graph.

Currently, the t-norms Minimum, Product and SoftmaxSum are provided.

[codecov]

Codecov Report

Attention: Patch coverage is 79.81651% with 22 lines in your changes missing coverage. Please review.

Project coverage is 72.13%. Comparing base (e7e9b8e) to head (be1586b).
Report is 14 commits behind head on main.

Files	Patch %	Lines
src/fuzzy/relations/continuous/old_tnorm.py	0.00%	16 Missing ⚠️
src/fuzzy/relations/continuous/t_norm.py	78.57%	3 Missing ⚠️
src/fuzzy/sets/continuous/group.py	0.00%	2 Missing ⚠️
src/fuzzy/relations/continuous/n_ary.py	98.70%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main       #2      +/-   ##
==========================================
+ Coverage   70.11%   72.13%   +2.01%     
==========================================
  Files          12       14       +2     
  Lines         716      793      +77     
==========================================
+ Hits          502      572      +70     
- Misses        214      221       +7     

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