Backport change to checkpoints format

[tomaka]

paritytech/substrate#9284 accidentally modified the checkpoints format. This PR backports this change.

We maintain compatibility with older checkpoints by not actually adding the new field but instead using decode instead of decode_all. Contrary to decode_all, decode succeeds even if there is data remaining after the decoded value, meaning that the additional field will not lead to an error.

This PR also updates the checkpoint in the Polkadot spec. I tested this PR with Westend (that uses an old checkpoint) and Polkadot (that uses a new checkpoint).

[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
─────────────┼──────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────────
        -615 ┊ smoldot::chain_spec::light_sync_state::_::<impl parity_scale_codec::codec::Decode for smoldot::chain_spec::light_sync_state::AuthoritySet>::decode::h6e81b20e098f6333
        +615 ┊ smoldot::chain_spec::light_sync_state::_::<impl parity_scale_codec::codec::Decode for smoldot::chain_spec::light_sync_state::AuthoritySet>::decode::hd5fa21b475a6a5ff
        +555 ┊ smoldot::chain_spec::light_sync_state::_::<impl parity_scale_codec::codec::Decode for smoldot::chain_spec::light_sync_state::BabeEpoch>::decode::h4e9508a1fad76102
        -555 ┊ smoldot::chain_spec::light_sync_state::_::<impl parity_scale_codec::codec::Decode for smoldot::chain_spec::light_sync_state::BabeEpoch>::decode::h8451f07c45ee4ec3
        -485 ┊ smoldot::chain_spec::light_sync_state::_::<impl parity_scale_codec::codec::Decode for smoldot::chain_spec::light_sync_state::PendingChange>::decode::h5d1802388957fd7e
        +485 ┊ smoldot::chain_spec::light_sync_state::_::<impl parity_scale_codec::codec::Decode for smoldot::chain_spec::light_sync_state::PendingChange>::decode::hec90a7f090f78772
        -467 ┊ smoldot::chain_spec::light_sync_state::_::<impl parity_scale_codec::codec::Decode for smoldot::chain_spec::light_sync_state::ForkTreeNode<T>>::decode::h881cea6f37472318
        +467 ┊ smoldot::chain_spec::light_sync_state::_::<impl parity_scale_codec::codec::Decode for smoldot::chain_spec::light_sync_state::ForkTreeNode<T>>::decode::hbe10b62b2fa0e982
        -418 ┊ smoldot::chain_spec::light_sync_state::_::<impl parity_scale_codec::codec::Decode for smoldot::chain_spec::light_sync_state::ForkTreeNode<T>>::decode::h255932ad5ef03be3
        +418 ┊ smoldot::chain_spec::light_sync_state::_::<impl parity_scale_codec::codec::Decode for smoldot::chain_spec::light_sync_state::ForkTreeNode<T>>::decode::h66ee4d6e7f189a7c
        -357 ┊ smoldot::chain_spec::light_sync_state::_::<impl parity_scale_codec::codec::Decode for smoldot::chain_spec::light_sync_state::PersistedEpoch>::decode::h42833c8fea41f164
        +357 ┊ smoldot::chain_spec::light_sync_state::_::<impl parity_scale_codec::codec::Decode for smoldot::chain_spec::light_sync_state::PersistedEpoch>::decode::h9a159a290e889a0f
        -347 ┊ smoldot::chain_spec::light_sync_state::_::<impl parity_scale_codec::codec::Decode for smoldot::chain_spec::light_sync_state::PersistedEpochHeader>::decode::h36613fcf15030f96
        +347 ┊ smoldot::chain_spec::light_sync_state::_::<impl parity_scale_codec::codec::Decode for smoldot::chain_spec::light_sync_state::PersistedEpochHeader>::decode::h7be5a88c53356026
        -292 ┊ <T as parity_scale_codec::decode_all::DecodeAll>::decode_all::ha32e6e93987d342d
        -258 ┊ <T as parity_scale_codec::decode_all::DecodeAll>::decode_all::hfcf1af9bfc31850a
        +256 ┊ smoldot::chain_spec::light_sync_state::_::<impl parity_scale_codec::codec::Decode for smoldot::chain_spec::light_sync_state::BabeAuthority>::decode::h560ed510626df89d
        -256 ┊ smoldot::chain_spec::light_sync_state::_::<impl parity_scale_codec::codec::Decode for smoldot::chain_spec::light_sync_state::BabeAuthority>::decode::hefa06c831bf36550
        -256 ┊ smoldot::chain_spec::light_sync_state::_::<impl parity_scale_codec::codec::Decode for smoldot::chain_spec::light_sync_state::GrandpaAuthority>::decode::h1d32ebbfa08bc530
        +256 ┊ smoldot::chain_spec::light_sync_state::_::<impl parity_scale_codec::codec::Decode for smoldot::chain_spec::light_sync_state::GrandpaAuthority>::decode::h2d2c5cb087f10545
         -60 ┊ ... and 11 more.
        -928 ┊ Σ [31 Total Rows]

[tomaka]

I've opened paritytech/polkadot-sdk#60

[melekes]

👍