Several fixes to metrics

[zouter]

• Add isomorphic and him
• Fixes for edge flip
• Only calculate geodesic distances when required
• Test the provided metrics
• FIxes for tests

[codecov[bot]]

Codecov Report

:exclamation: No coverage uploaded for pull request base (master@ea685f8). Click here to learn what that means. The diff coverage is 69.15%.

@@            Coverage Diff            @@
##             master      #41   +/-   ##
=========================================
  Coverage          ?   86.78%           
=========================================
  Files             ?        8           
  Lines             ?      522           
  Branches          ?        0           
=========================================
  Hits              ?      453           
  Misses            ?       69           
  Partials          ?        0

Impacted Files	Coverage Δ
R/metric_him.R	0% <0%> (ø)
R/calculate_metrics.R	78.76% <50%> (ø)
R/metric_flip.R	89.8% <98.27%> (ø)

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