Add a blockNumberBytes field in chain specs

[tomaka]

cc #2478

The change is rather straight forward: we add a new optional blockNumberBytes field in the chain specs format and pass its value around. The value defaults to 4 if it's missing.

[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.

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 Delta Bytes │ Item
─────────────┼─────────────────────────────────────────────────────────────────────────────────────────────────────────────
       +4227 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::hb10ed4dababbd50c
       -4214 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::h14ece9dd36df2cd6
       +3226 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::h2498be66670d547f
       -3122 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::ha40c4403a162aba0
       -2136 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::h78455e4882c3a983
       +2135 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::h9bc060acb423dd39
       +1327 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::he50e7bf7341f20a0
       -1296 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::hd72e904c63df3033
       +1018 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::h4546461ffef36006
       -1018 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::hc4be4ba165e4506e
        -945 ┊ <futures_util::future::future::shared::Shared<Fut> as core::future::future::Future>::poll::ha3978bf09d40e019
        +945 ┊ <futures_util::future::future::shared::Shared<Fut> as core::future::future::Future>::poll::hf2400c46d828d658
        +711 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::h6771f3fbb8df3a52
        -711 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::ha7c0f35a711f8e98
        +671 ┊ <serde_json::de::MapAccess<R> as serde::de::MapAccess>::next_key_seed::h070195c8739260ea
        -671 ┊ <serde_json::de::MapAccess<R> as serde::de::MapAccess>::next_key_seed::h105432efc18949c5
        +550 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::h39c87466f56e82f3
        -550 ┊ <core::future::from_generator::GenFuture<T> as core::future::future::Future>::poll::h7b73015b0b805350
        -513 ┊ futures_channel::oneshot::Inner<T>::send::hc4ae0a5e3b748553
        -466 ┊ futures_util::future::future::shared::Inner<Fut>::take_or_clone_output::h68e861dfff5217b5
        +997 ┊ ... and 184 more.
        +503 ┊ Σ [204 Total Rows]