[utils] Create abstraction over a sorted vec

[cronokirby]

In a few places, we need to map between a set of items and the indices [0..num_items] example 1, also the DKG / Reshare.

We do this with an ad-hoc abstraction in each case, but it would be useful to have a little abstraction in utils for this.

A simple way to do this would be to have the backing type contain a sorted vec of elements. You could easily create this from a slice or iterator, by collecting the elements, sorting them, and then removing duplicates. You could map an index to an item in O(1), by just indexing into the vector, and you could figure the index of an item with a binary search.

[patrick-ogrady]

and then removing duplicates

I think it may be nice to make this configurable? 🤔

[patrick-ogrady]

Very very supportive of using a proper type for this. I'm terrified of forgetting to call .sort() on some input somewhere of the participants...

[cronokirby]

and then removing duplicates

I think it may be nice to make this configurable? 🤔

Maybe, but if you have duplicates, you no longer have a 1-to-1 mapping from items to indices, but instead a 1-to-many mapping, with each item having multiple indices. The latter might be useful in some cases, but seems like a footgun in others.

Maybe the configurability is to return an Option with duplicates instead of just removing them silently?