Incorrect move pos detection

[Freak613]

I have a case for a list of 10 elements, swapping list[1] and list[8] to each other

var tmp = list[1]
list[1] = list[8]
list[8] = tmp

Library incorrectly detects everything between 1 and 8 idx as moved and produces 8 MOVE effects, with prev = next for [2-7] elements. Elements in between has the same indices and it should produce UPDATE for them.

[leeoniya]

when i fuzzed dift, i also saw many correctness issues. kinda made me question its claims, especially

dift has not just extensive tests but exhaustive tests