Optimize prefix_proof by reducing the number of iterations

[tomaka]

cc #351

[github-actions]

twiggy diff report

Difference in .wasm size before and after this pull request.

---

 Delta Bytes │ Item
─────────────┼────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
       -1353 ┊ alloc::slice::merge_sort::h419549773d9f3902
        +714 ┊ smoldot::trie::prefix_proof::PrefixScan::resume::h8c4c7b1729d58659
        +620 ┊ <core::iter::adapters::map::Map<I,F> as core::iter::traits::iterator::Iterator>::fold::h093532650fc1509c
        -620 ┊ <core::iter::adapters::map::Map<I,F> as core::iter::traits::iterator::Iterator>::fold::h4f899e96ba7b60d4
        +523 ┊ smoldot::trie::proof_decode::DecodedTrieProof<T>::children_from_key::h592c139d7b1c5a77
        +495 ┊ <core::iter::adapters::chain::Chain<A,B> as core::iter::traits::iterator::Iterator>::fold::h1bd8c062df03b630
        +495 ┊ <core::iter::adapters::chain::Chain<A,B> as core::iter::traits::iterator::Iterator>::fold::h2e994c18236b7475
        -495 ┊ <core::iter::adapters::chain::Chain<A,B> as core::iter::traits::iterator::Iterator>::fold::h5a16279a7101c26f
        -495 ┊ <core::iter::adapters::chain::Chain<A,B> as core::iter::traits::iterator::Iterator>::fold::h69807c3b232f99a1
        -486 ┊ <core::iter::adapters::chain::Chain<A,B> as core::iter::traits::iterator::Iterator>::fold::h3d4641880a4ed2f6
        +486 ┊ <core::iter::adapters::chain::Chain<A,B> as core::iter::traits::iterator::Iterator>::fold::h51ab3f07d8899627
        +461 ┊ smoldot::trie::proof_decode::DecodedTrieProof<T>::children_from_key::h35940ce888e913f6
        +438 ┊ smoldot::trie::proof_decode::DecodedTrieProof<T>::children_from_key::heb071a43d22e9cc0
        +435 ┊ <core::iter::adapters::chain::Chain<A,B> as core::iter::traits::iterator::Iterator>::fold::h5e9ec52f35cae481
        -435 ┊ <core::iter::adapters::chain::Chain<A,B> as core::iter::traits::iterator::Iterator>::fold::h67bf0189dd0de171
        -349 ┊ <core::iter::adapters::map::Map<I,F> as core::iter::traits::iterator::Iterator>::fold::h097266e1e57acf14
        +346 ┊ <core::iter::adapters::map::Map<I,F> as core::iter::traits::iterator::Iterator>::fold::h4c43485ec6f6e1dd
        -306 ┊ alloc::slice::merge::he2d896d72f357fc6
        +274 ┊ smoldot::network::service::requests_responses::<impl smoldot::network::service::ChainNetwork<TNow>>::start_storage_proof_request::h95ddab53f931a453
        -274 ┊ smoldot::network::service::requests_responses::<impl smoldot::network::service::ChainNetwork<TNow>>::start_storage_proof_request::hcd94cb3779db4290
        +601 ┊ ... and 107 more.
       +2256 ┊ Σ [127 Total Rows]