Become compatible with new codeSubstitutes

[tomaka]

cc #1844

This PR makes us compatible with both old and new chain specs. This is possible because the field is currently unused and private.

After a new version of smoldot is released, the chain specs can be updated, and then later we can remove the hexadecimal.

[mergify]

Automatically approving tomaka's pull requests. This auto-approval will be removed once more maintainers are active.

[github-actions]

twiggy diff report

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

---

 Delta Bytes │ Item
─────────────┼────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
        -563 ┊ <smoldot::chain_spec::structs::HashHexString as serde::de::Deserialize>::deserialize::h12fc58a126ea2eb9
        +563 ┊ <smoldot::chain_spec::structs::HashHexString as serde::de::Deserialize>::deserialize::h59d0d4f6e1d693a0
        +533 ┊ <serde_json::de::MapAccess<R> as serde::de::MapAccess>::next_key_seed::h3ab70ad99c3c2447
        +531 ┊ <&mut serde_json::de::Deserializer<R> as serde::de::Deserializer>::deserialize_map::h17863bd6ba27fce9
        -531 ┊ <&mut serde_json::de::Deserializer<R> as serde::de::Deserializer>::deserialize_map::hb680ab0c1a6763e7
        -477 ┊ <hashbrown::external_trait_impls::serde::map::<impl serde::de::Deserialize for hashbrown::map::HashMap<K,V,S>>::deserialize::MapVisitor<K,V,S> as serde::de::Visitor>::visit_map::hf9449ee7280655f1
        -443 ┊ hashbrown::raw::RawTable<T,A>::rehash_in_place::h24096112729f20b0
        +443 ┊ hashbrown::raw::RawTable<T,A>::rehash_in_place::he4543ad002fa83c1
        +438 ┊ <smoldot::chain_spec::structs::NumberAsString as serde::de::Deserialize>::deserialize::h21311e9522bc9f57
        +419 ┊ hashbrown::raw::RawTable<T,A>::resize::h4605f067c0226c48
        -419 ┊ hashbrown::raw::RawTable<T,A>::resize::h785398ece67b789f
        -346 ┊ hashbrown::map::HashMap<K,V,S,A>::insert::h091ab0e3a6e18ef3
        +338 ┊ <hashbrown::external_trait_impls::serde::map::<impl serde::de::Deserialize for hashbrown::map::HashMap<K,V,S>>::deserialize::MapVisitor<K,V,S> as serde::de::Visitor>::visit_map::heb2365a2c750ff6e
        +320 ┊ hashbrown::map::HashMap<K,V,S,A>::insert::hcddc5596130f60ea
        -293 ┊ hashbrown::raw::RawTable<T,A>::clone_from_impl::h2f9278aa8dad389b
        +284 ┊ hashbrown::raw::RawTable<T,A>::clone_from_impl::h66f5e9bd6498d277
        +265 ┊ core::num::<impl core::str::traits::FromStr for u64>::from_str::h56657c92abb38cc3
        +191 ┊ hashbrown::raw::RawTable<T,A>::insert::h67bb7142bc404961
        -191 ┊ hashbrown::raw::RawTable<T,A>::insert::h91c6c5b4f922bc89
        -189 ┊ <hashbrown::raw::RawIterRange<T> as core::iter::traits::iterator::Iterator>::next::h3841cb5c5e0e81fa
        +300 ┊ ... and 87 more.
        +761 ┊ Σ [107 Total Rows]