Optionalshards_Maps shards from the last shard layout to shards that it splits to in this shard layout, Useful for constructing states for the shards. None for the genesis shard layout
Optionalto_Maps shard in this shard layout to their parent shard Since shard_ids always range from 0 to num_shards - 1, we use vec instead of a hashmap
Version of the shard layout, this is useful for uniquely identify the shard layout
The boundary accounts are the accounts on boundaries between shards. Each shard contains a range of accounts from one boundary account to another - or the smallest or largest account possible. The total number of shards is equal to the number of boundary accounts plus 1.