perf(root): chunk proof targets in state root task

[shekhirin]

Towards #14417

Given proof targets with 100 accounts, it's preferred to spawn 20 multiproofs with 5 accounts each, instead of spawning one multiproof for all 100 accounts at once. The reason for that is that 20 multiproofs can be executed in parallel (even considering that they may do redundant work because of the intersecting trie nodes), while one multiproof will be executed serially for all accounts.

Same idea can be applied to storage slots: proof targets with 1 account and 100 storage slots is better spawned as 5 multiproofs for 20 storage slots each, rather than one multiproof for all 100 storage slots at once.

This PR adds chunking on the StateRootTask side, so that every set of proof targets is broken into multiple state updates using ChunkedProofTargets iterator, and spawned as a separate multiproof. This is applied to both on_prefetch_proof and on_state_update

[jenpaff]

link #14417