granular test for nodes.fix_topology()

[jGaboardi]

This PR:

• adds a granular test for nodes.fix_topology()
  • xref testing, refactor, & docstrings #20
  • xref start testing + refactor [stub issue] #21
• clean index after nodes.fix_topology()
  • resolves clean integer index when returning nodes.remove_false_nodes() #90

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 98.4%. Comparing base (82cd59e) to head (29839e7).
Report is 1 commits behind head on main.

Additional details and impacted files

@@          Coverage Diff          @@
##            main     #91   +/-   ##
=====================================
  Coverage   98.4%   98.4%           
=====================================
  Files          6       6           
  Lines        923     923           
=====================================
  Hits         908     908           
  Misses        15      15           

Files with missing lines	Coverage Δ
sgeop/nodes.py	99.0% <100.0%> (ø)