Implement add_node_to_edge and remove_node_from_edge for DiHypergraphs

[nwlandry]

This adds the ability to add/remove nodes to/from a directed hyperedge.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 92.51%. Comparing base (d7a90a7) to head (7898eaa).
Report is 2 commits behind head on main.

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #571   +/-   ##
=======================================
  Coverage   92.51%   92.51%           
=======================================
  Files          59       59           
  Lines        4393     4394    +1     
=======================================
+ Hits         4064     4065    +1     
  Misses        329      329           

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[nwlandry]

@maximelucas are you still able to review this?

[nwlandry]

In the interest of time, and since all modified lines are covered by tests, I am merging this.