Add LineDigraph transformation

[petern48]

Addresses #9457 in collaboration with @Flunzmas

Changes:

• Implement an optimized transforms module for LineDiGraph based off of the implementation by Bernárdez et al.
• Add a test for testing the implementation

Motivation from Flunzmas:

Recent scientific work [1] leveraging GNNs for routing in computer networks has used a line digraph representation of the computer network topology as input for their GNN policies. The line digraph is formed by taking the original graph's edges as new nodes, and drawing an edge between those new nodes that, as edges in the original graph, form a directed path of length two: E' = {(u, v), (w, x) | (u, v) in E; (w, x) in E; v = w}.

[1]: Bernárdez et al. "Magnneto: A graph neural network-based multi-agent system for traffic engineering." IEEE Transactions on Cognitive Communications and Networking 9.2 (2023)

[petern48]

@rusty1s Do I need to do anything to update the docs? I thought it would produce the page automatically, but I don't see it in the built docs.

[Flunzmas]

Hi, I am reviving this MR by adding an option to put the node features of the original graph into the line digraph's edge features.

Let us know if there is anything missing to conclude this MR 🙂.