YT-CPPGL-68: Implement missing vertex view getters

[SpectraL519]

• Extended the graph class with missing vertex collection getters:
  • Descriptor getters: neighbors, predecessors, successors
  • ID getters: neighbor_ids, predecessor_ids, successor_ids
• Fixed the incident_edges logic error:
  • Previously the function always called out_edges, which is correct for undirected graphs but not for directed graphs
  • Extended the internal implementation classes with specific incident edges getters
  • Aligned the graph class methods to use the proper underlying implementation type's methods
• Changed the are_incident method names for vertex pairs and edge pairs to use the proper term (are_adjacent)
• Cleaned up the layout of methods in the graph class and the implementation classes
• Cleaned up the gl module tests

[SpectraL519]

My eyes hurt and I don't have the energy to read all of this as there is a lot of moving things around without changing them but the diff is quite large because of this and so I will let AI do the review

[SpectraL519]

OK