Add weighted graph types about rustworkx HOT 2 CLOSED

I'm not sure there is going to actually be a need for this moving forward. We can use a python callback to return a fixed type that has a built in pyo3 conversion to a rust type for algorithms that need a weight. For example, what I did with the weight_fn in #75. This lets us keep the usage of the weight to rust and just have the python code return a known type which can minimize the python side overhead so something like just an attribute return of a cast. While not as fast as a pure rust implementation this should be a fair tradeoff with flexibility.

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Based on my earlier comment, I'm going to close this. We can reopen and revisit if there is a need for a statically typed (from the python perspective) weighted graph, but for right now the callback approach works well and the overhead doesn't seem to be a huge deal especially if a sane callback is used.

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