Removing a vertex from an UndirectedSparseGraph is very slow, make it faster

[melon3r]

Is your feature request related to a problem? Please describe. In an application, I have to create an UndirectedSparseGraph from which I then filter out (i.e. RemoveVertex) many nodes, which takes minutes for a graph of less than a thousand vertices.

Describe the solution you'd like Optimally, this should be taking seconds, instead of minutes. I've created a pull request that achieves this: https://github.com/aalhour/C-Sharp-Algorithms/pull/130/

[github-actions[bot]]

Thanks for supporting the development of C# Algorithms with your first issue! We look forward to handling it.