Hypergat layer edge attention fix pr

[tz545]

In the HyperGat paper, the second attention calculation should compute the edge-level attention. The attention function in hypergat_layer.py computes a node-level attention by default, so here the mechanism "edge_level" should be explicitly specified on line 203.

Additionally, in line 116 in the attention function, I believe self.target_index_i $\in [0, N]$ should be changed to self.source_index_j $\in [0, E]$ in node-level attention (where $N$ is the number of nodes and $E$ is the number of hyperedges), as the input for node-level attention has dimensions (E, h_dim).

Similarly, line 125 should be changed to index a node, and line 129 should index an edge.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 97.37%. Comparing base (fd6ad4f) to head (aa9ecd2).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #337   +/-   ##
=======================================
  Coverage   97.37%   97.37%           
=======================================
  Files          58       58           
  Lines        2060     2060           
=======================================
  Hits         2006     2006           
  Misses         54       54           

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