[ashishsoni-ai]

Description

This PR enhances \devograph.base_graph.BaseGraph, the core graph data structure in DevoGraph, by adding essential topology query methods, hypergraph matrix representations for GNN models, removal operations, and serialization support.

Previously, \BaseGraph\ provided only basic \�dd_node, \�dd_edge,
um_nodes, and
um_edges. Downstream pipelines in DevoGraph (such as \Dynamic-HGNN\ and \HyperDevoGraph) require querying node neighborhoods, computing node degrees, generating hypergraph incidence matrices, and exporting PyG-compatible edge indices.

Changes Made

1. Node and Edge Queries:

   • \has_node(node_id): verify node membership.
   • \get_node(node_id): retrieve node attribute dictionary.
   • \get_nodes(): list all node IDs.
   • \has_edge(node_ids): check for the existence of an edge or hyperedge.
   • \get_edge(index)\ and \get_edges(): access edge records.

2. Graph Topology Operations:

   • 
     eighbors(node_id): retrieve all neighboring nodes connected via pairwise edges or multi-node hyperedges.
   • \degree(node_id): count incident edges / hyperedges for a node.
   • \incident_edges(node_id): list edge indices incident to a given node.
   • 
     emove_node(node_id): remove a node and prune all incident edges.
   • 
     emove_edge(index): remove an edge by index.

3. Hypergraph & GNN Matrix Exports:

   • \ o_incidence_matrix(): returns an (N, E)\ binary matrix (H) where (H_{i, j} = 1) if node (i) belongs to edge/hyperedge (j). This directly supports Hypergraph Neural Networks (HGNN / Hyper-SAGNN).
   • \ o_adjacency_matrix(weighted=False): generates an (N, N)\ adjacency matrix using clique expansion for hyperedges of size > 2.
   • \ o_edge_index(bidirectional=True): exports edge index array of shape (2, E)\ in PyTorch Geometric (PyG) format.

4. Serialization & Magic Methods:

   • \ o_dict()\ and \rom_dict(): serialization round-trip to easily save/load graphs in JSON/dict format.
   • _len_(): returns node count.
   • _repr_(): clean string representation (\BaseGraph(num_nodes=..., num_edges=...)).

5. Top-Level Package Export:

   • Exported \BaseGraph\ in \devograph/init.py\ for \rom devograph import BaseGraph.

6. Comprehensive Unit Testing:

   • Added 9 unit tests in \ est/test_base_graph.py\ verifying all query methods, matrix conversions, hyperedge handling, error checks, and dictionary round-trip serialization.
   • All tests pass: \pytest test/test_base_graph.py.