Fix #200: [Rule] MinimumVertexCover to MinimumHittingSet

[zazabap]

Summary

• Add reduction from MinimumVertexCover<SimpleGraph, One> to MinimumHittingSet
• Register unit-weight MVC variant (MinimumVertexCover<SimpleGraph, One>)
• Connect the orphaned MinimumHittingSet node to the reduction graph

Fixes #200

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 97.85%. Comparing base (f29cfb1) to head (6cd8d50).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #793   +/-   ##
=======================================
  Coverage   97.85%   97.85%           
=======================================
  Files         625      625           
  Lines       68311    68311           
=======================================
  Hits        66846    66846           
  Misses       1465     1465           

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