Add a cache for state_getKeysPaged requests

[tomaka]

cc #351

[github-actions]

twiggy diff report

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

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 Delta Bytes │ Item
─────────────┼─────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
       +6699 ┊ smoldot_light::json_rpc_service::background::Background<TPlat>::runtime_lock::{{closure}}::h9d628d058b3986f8
       -6699 ┊ smoldot_light::json_rpc_service::background::Background<TPlat>::runtime_lock::{{closure}}::hb9601494b95dbab3
       -2119 ┊ futures_util::abortable::Abortable<T>::try_poll::h12278d4e1fcbf895
       +2119 ┊ futures_util::abortable::Abortable<T>::try_poll::h61ea2ba7b294a3d8
       +1192 ┊ smoldot_light::json_rpc_service::background::Background<TPlat>::state_trie_root_hash::{{closure}}::hdbf455a661796e3d
       -1192 ┊ smoldot_light::json_rpc_service::background::Background<TPlat>::state_trie_root_hash::{{closure}}::hfea723335250adb0
       +1022 ┊ smoldot_light::json_rpc_service::background::Background<TPlat>::handle_request::{{closure}}::hf803cfc2f8737078
        +484 ┊ lru::LruCache<K,V,S>::capturing_put::h945d1c535b67f71b
        +463 ┊ hashbrown::raw::RawTable<T,A>::reserve_rehash::h3543502624f55175
        +366 ┊ lru::LruCache<K,V,S>::replace_or_create_node::h06f88b7315d660e3
        -360 ┊ <core::iter::adapters::map::Map<I,F> as core::iter::traits::iterator::Iterator>::try_fold::h70fca7cc718a17be
        +309 ┊ core::ptr::drop_in_place<smoldot_light::json_rpc_service::background::state_chain::<impl smoldot_light::json_rpc_service::background::Background<smoldot_light_wasm::platform::Platform>>::state_get_keys_paged::{{closure}}>::h5178600ea652a378
        -297 ┊ core::ptr::drop_in_place<futures_util::abortable::Abortable<smoldot_light::json_rpc_service::background::start<smoldot_light_wasm::platform::Platform>::{{closure}}>>::h3339986ee932f72f
        +297 ┊ core::ptr::drop_in_place<futures_util::abortable::Abortable<smoldot_light::json_rpc_service::background::start<smoldot_light_wasm::platform::Platform>::{{closure}}>>::h7d15a7919315e14d
        +266 ┊ futures_util::lock::mutex::Mutex<T>::remove_waker::h540509be2642ac7e
        -266 ┊ futures_util::lock::mutex::Mutex<T>::remove_waker::h634fcd083097b995
        +250 ┊ core::ptr::drop_in_place<smoldot_light::json_rpc_service::background::Background<smoldot_light_wasm::platform::Platform>::runtime_lock::{{closure}}>::h4dfede76173df05f
        -250 ┊ core::ptr::drop_in_place<smoldot_light::json_rpc_service::background::Background<smoldot_light_wasm::platform::Platform>::runtime_lock::{{closure}}>::he7db6f41156b6cad
        +235 ┊ <alloc::vec::Vec<T> as alloc::vec::spec_from_iter_nested::SpecFromIterNested<T,I>>::from_iter::h020c150221b29530
        -207 ┊ core::ptr::drop_in_place<smoldot_light::json_rpc_service::background::state_chain::<impl smoldot_light::json_rpc_service::background::Background<smoldot_light_wasm::platform::Platform>>::state_get_keys_paged::{{closure}}>::h3b0283282c0ab07e
       +2643 ┊ ... and 77 more.
       +7877 ┊ Σ [97 Total Rows]