`rand_mutate` cannot generate consecutive insertions about block-aligner

[Daniel-Liu-c0deb0t]

Good point, this is an oversight on my part. I think it does matter in practice because chains of insertions and deletions makes finding the optimal alignment slightly more difficult for block aligner.

[RagnarGrootKoerkamp]

One potential benefit here is that the actual edit distance of the generated sequence is probably a bit higher than in the completely uniform model. At least my intuition is that in your code the probability of mutations 'cancelling' each other is smaller.

Anyway, I'll likely write a linear time rust implementation for this soon.

[RagnarGrootKoerkamp]

I've just pushed an implementation using ropes here, in case you'd like to reuse it. I'll likely package it separately at some point.

[Daniel-Liu-c0deb0t]

Fixed the implementation of the rand_mutate function by using a slightly different approach than before.