testing and small refactor -- nodes.consolidate_nodes()

[jGaboardi]

This MR:

• resolves remove legacy line in nodes.consolidate_nodes() #96
• xref testing, refactor, & docstrings #20
• xref start testing + refactor [stub issue] #21
• add specific testing cases for nodes.consolidate_nodes()

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.5%. Comparing base (41f7d97) to head (0e14999).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##            main     #97     +/-   ##
=======================================
+ Coverage   98.4%   98.5%   +0.1%     
=======================================
  Files          6       6             
  Lines        923     923             
=======================================
+ Hits         908     909      +1     
+ Misses        15      14      -1     

Files with missing lines	Coverage Δ
sgeop/nodes.py	99.5% <100.0%> (+0.5%)	⬆️

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