[ENH] Adding multi-domain functional linear graph and fix bug related to drawing causal graphs

[adam2392]

Fixes: #76

Changes proposed in this pull request:

• add ability to convert linear functional graph into a multiple domain setting

The API leverages the graph dictionary data structure inside it to store metadata about the multi-domain setting:

• of domains

It also leverages the node_attributes to store the following for linear-graphs for each node:

{
            'X': {
                'parent_functions': {
                    'Y': {
                        'weight': <weight of Y added to X>,
                        'func': <function that takes input Y>,
                    },
                    'Z': {
                        'weight': <weight of Z added to X>,
                        'func': <function that takes input Z>,
                    },
                },
                'gaussian_noise_function': {
                    'mean': <mean of gaussian noise added to X>,
                    'std': <std of gaussian noise added to X>,
                }
            }
        }

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  Writing docstrings section of the CONTRIBUTING docs.
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[codecov-commenter]

Codecov Report

Merging #77 (ade5c07) into main (3de911e) will decrease coverage by 4.58%.
The diff coverage is 41.88%.

@@            Coverage Diff             @@
##             main      #77      +/-   ##
==========================================
- Coverage   84.59%   80.02%   -4.58%     
==========================================
  Files          35       39       +4     
  Lines        2590     2838     +248     
  Branches      698      759      +61     
==========================================
+ Hits         2191     2271      +80     
- Misses        247      408     +161     
- Partials      152      159       +7     

Impacted Files	Coverage Δ
pywhy_graphs/functional/multidomain.py	11.57% <11.57%> (ø)
pywhy_graphs/algorithms/multidomain.py	50.00% <50.00%> (ø)
pywhy_graphs/classes/augmented.py	69.42% <54.23%> (ø)
pywhy_graphs/functional/utils.py	56.52% <56.52%> (ø)
pywhy_graphs/functional/linear.py	66.66% <57.69%> (-19.05%)	⬇️
pywhy_graphs/viz/draw.py	76.92% <66.66%> (+3.58%)	⬆️
pywhy_graphs/functional/additive.py	76.47% <76.47%> (ø)

... and 1 file with indirect coverage changes

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