Optimize a bit bfs and dfs iterators

[Tortar]

in particular, bfs is like 40% faster

[codecov[bot]]

Codecov Report

All modified and coverable lines are covered by tests :white_check_mark:

Project coverage is 97.31%. Comparing base (43f9f18) to head (7e5f2a8).

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #381 +/- ## ======================================= Coverage 97.31% 97.31% ======================================= Files 120 120 Lines 6954 6956 +2 ======================================= + Hits 6767 6769 +2 Misses 187 187 ```

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[simonschoelly]

I see why dfs should always be faster, as there the only improvement there is using @inbound and the rest seems to be renaming. For bfs a statement like makes it 40% faster needs some explanation. At least on what kind of graphs - but better with the whole benchmark setup.

I am saying this, because we also had the case, that people just tested performance on graphs that did not really fit the problem. Therefore I think we should publish the whole methodology when testing for speedup

[Tortar]

closing in favour of #382