Eliminate recursion with a fixed-size stack

[mourner]

Managed to get a perf win with recursion elimination here too — but in a simpler/faster way, by only increasing the stack once on each illegal edge. cc @delfrrr

[delfrrr]

Need to spend time on it to understand why it will produce the same result 😯

[mourner]

@delfrrr basically, it "recurses" (increases stack) only in one direction, while the other one just runs as the next iteration of the loop (while keeping a value).