Implement array diff using Myers' algorithm

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Diffing arrays is particularly inefficient when changes trigger the full LCS algorithm. Implementing Myers' algorithm should be a significant speed-up.

(Leaving this as a note for myself, no time to tackle the issue right now.)

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003348f implements greedy search, without refinements, as described in the paper.

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Unassigned myself, because I currently don't have a need to implement additional performance improvements in array diffing.