[POP-2983] Batch oblivious array minimum

[iliailia]

No description provided.

[sdwoodbury]

not related to this PR: I think I found a way to remove a clone() in oblivious_min_distance()

[sdwoodbury]

Nice!

I left a comment about a potential optimization. It isn't blocking though.

[sdwoodbury]

Suggested change

	let pairs = res
	.chunks_exact(2)
	.flat_map(|chunk| izip!(chunk[0].clone(), chunk[1].clone()).collect_vec())
	.collect_vec();
	// compute minimums of pairs
	let flattened_res = min_of_pair_batch(&mut self.session, &pairs).await?;
	res = flattened_res
	.chunks_exact(len)
	.map(|chunk| chunk.to_vec())
	.collect_vec();
	let mut res1 = vec![];
	std::mem::swap(&mut res1, &mut res);
	let pairs: Vec<(_, _)> = res1
	.into_iter()
	.tuples()
	.flat_map(|(a, b)| izip!(a, b).collect_vec())
	.collect();
	// compute minimums of pairs
	let flattened_res = min_of_pair_batch(&mut self.session, &pairs).await?;
	res = flattened_res
	.into_iter()
	.chunks(len)
	.into_iter()
	.map(|chunk| chunk.collect())
	.collect_vec();

[iliailia]

Nice! Thanks!