rust: storage/seg - implement an iterator for item info

[brayniac]

In the hashtable module, we are frequently iterating through the hash buckets and info slots to get item info. This is a lot of duplicate code that feels like it can be more concisely expressed at the call sites as an iterator.

[hderms]

@brayniac are you referring to iterations like this repeated chunk:

pelikan/src/rust/storage/seg/src/hashtable/mod.rs

Lines 307 to 318 in 13b1b3a

	for chain_idx in 0..=chain_len {
	let n_item_slot = if chain_idx == chain_len {
	N_BUCKET_SLOT
	} else {
	N_BUCKET_SLOT - 1
	};
	for i in 0..n_item_slot {
	if chain_idx == 0 && i == 0 {
	continue;
	}
	let current_info = bucket.data[i];

[brayniac]

@hderms - yes. It feels like we can provide an iterator where the iterator's item type is ItemInfo which would be a new type