YT-CPPHGL-7: Implement the undirected vertex-list model

[SpectraL519]

• Created the impl::undirected_vertex_list model class, which stores a list of vertices and their incident hyperedges and define the following operations:
  • Adding and removing vertices
  • Adding and removing hyperedges
  • Binding and unbinding vertices to hyperedges
  • Retrieving the degree of a vertex
  • Retrieving the set of hyperedges incident with (containing) a given vertex
  • Retrieving the number of vertices incident with a given hyperedge
  • Retrieving the set of vertices incident with a given hyperedge
• Renamed the impl::adjacency_list_t tag to impl::vertex_list_t
• Added missing methods to the impl::undirected_hyperedge_list class
• Aligned the vertex removal logic in the hyperedge-list model to properly unbind the given vertex from all edges and decrement the ids, which are greater than the given vertex id

[SpectraL519]

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