perf(graph-algos): optimize neighbor filtering in SCC with HashSet lookup

[0xxFloki]

Optimize get_neighbors_in_given_scc by replacing O(n²) Vec scanning with O(n) HashSet lookup.

[reviewable-StarkWare]

This change is 

[orizi]

@orizi made 1 comment.
Reviewable status: 0 of 1 files reviewed, 1 unresolved discussion (waiting on @0xxFloki).

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a discussion (no related file):
in the general case - probably correct.

at our normal case - would be much slower. as the scc sets are usually extremely small, hash maps are basically just a big waste.
(as linear search is more efficient up until ~200 elements)