Parameterize Sigma over the Graph type

[lf-]

This allows for getting the Graph as an object with typed attributes, allowing for type-safely accessing properties through it.

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• [x] Feature
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What is the current behavior?

You currently have to create a subclass to put custom data on nodes/edges and have it be type safe.

What is the new behavior?

It's now possible to just specify the exact graph type as a type parameter and it will work.

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