I just skimmed it but this seems to be the practical lesson for coders:
As mentioned previously, adding a call to shrink_to_fit() prior to storing the edge lists in the final graph eliminated the memory leak issue. This is fine as a quick hack, but it is not the proper solution. The real fix is to call into_boxed_slice() instead.
The basic problem is that Vecs are optimized for the case of a mutable list where you’re planning to add and remove elements in the future. However, people also commonly use them for fixed-length list data, even though this is not what Vecs are designed for, simply because Vec is the easiest and most intuitive way to store list data in Rust. The proper data structure for fixed-length lists is Box<[T]> rather than Vec<T>, but it takes a lot of Rust experience to even know about that as an option, and the syntax looks weirder.