[MAINT] Improve some tests and refactor dev experience to be in line w/ dowhy

[adam2392]

Changes proposed in this pull request:

• Add a unit test to make sure tuple nodes work as expected
• Change apply_format to format, which is the same in dowhy

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  section of the CONTRIBUTING docs.
• I've updated or added any relevant docstrings following the syntax described in the
  Writing docstrings section of the CONTRIBUTING docs.
• If this PR fixes a bug, I've added a test that will fail without my fix.
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[codecov-commenter]

Codecov Report

Merging #74 (dc72551) into main (c387f8a) will increase coverage by 0.38%.
The diff coverage is 71.49%.

@@            Coverage Diff             @@
##             main      #74      +/-   ##
==========================================
+ Coverage   84.03%   84.42%   +0.38%     
==========================================
  Files          29       34       +5     
  Lines        2255     2555     +300     
  Branches      578      687     +109     
==========================================
+ Hits         1895     2157     +262     
+ Misses        254      251       -3     
- Partials      106      147      +41     

Impacted Files	Coverage Δ
pywhy_graphs/classes/admg.py	95.12% <ø> (ø)
pywhy_graphs/classes/cpdag.py	83.67% <ø> (ø)
pywhy_graphs/classes/pag.py	82.25% <ø> (ø)
pywhy_graphs/export/tigramite.py	0.00% <0.00%> (ø)
pywhy_graphs/testing.py	50.00% <50.00%> (ø)
pywhy_graphs/export/pcalg.py	55.04% <55.04%> (ø)
pywhy_graphs/export/tetrad.py	68.75% <68.75%> (ø)
pywhy_graphs/classes/intervention.py	88.17% <71.42%> (-3.72%)	⬇️
pywhy_graphs/export/numpy.py	72.85% <72.85%> (ø)
pywhy_graphs/export/causallearn.py	79.22% <80.95%> (ø)
... and 3 more

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