Add edge-count consistency checks in test_graph_creation

[Shivampal157]

Describe your changes

Add edge-count consistency checks in test_graph_creation: the test now asserts that for each graph (g2m, m2g, m2m, and for hierarchical graphs mesh_up / mesh_down), the number of edges in each *_edge_index.pt file matches the number of rows in the corresponding *_features.pt file. This addresses the outstanding TODO in the test file.

No new dependencies. Motivation: ensure generated graph files are internally consistent before they are used downstream.

Issue Link

Closes #380

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• 🐛 Bug fix (non-breaking change that fixes an issue)
• ✨ New feature (non-breaking change that adds functionality)
• 💥 Breaking change (fix or feature that would cause existing functionality to not work as expected)
• 📖 Documentation (Addition or improvements to documentation)

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[Shivampal157]

@sadamov , I’ve implemented the edge-count consistency checks for issue #380 and opened a PR. Could you take a look when you have time?

[Sharkyii]

@Shivampal157 the code LGTM, just revert back to the original PR template

[Shivampal157]

@joeloskarsson @Sharkyii Done, reverted to the original PR template. Thanks.

[joeloskarsson]

It looks like we have duplicate fixes for this in #301 and #396 now. Please discuss in #380 how to best solve this.

[joeloskarsson]

Closed in favor of #301