Starlight <> Ethereum: Rewards mapping

[Agusrodri]

What does it do?

This PR takes care of generating a specific command called ReportRewards, which is used to map and encode rewards data happening in Starlight. This information will then be used by Symbiotic smart contracts on the Ethereum side to perform specific computation/checks related to rewards.

More specifically, the ReportRewards command has the following structure:

    ReportRewards {
        // block timestamp
        timestamp: u64,
        // index of the era we are sending info of
        era_index: u32,
        // total_points for the era
        total_points: u128,
        // new tokens inflated during the era
        tokens_inflated: u128,
        // merkle root of vec![(validatorId, rewardPoints)]
        rewards_merkle_root: H256,
    }

Addition of runtime api

In this PR, a ExternalValidatorsRewardsApi runtime api was added, containing two main functions:

sp_api::decl_runtime_apis! {
    pub trait ExternalValidatorsRewardsApi<AccountId, EraIndex>
    where
        AccountId: parity_scale_codec::Codec,
        EraIndex: parity_scale_codec::Codec,
    {
        fn generate_rewards_merkle_proof(account_id: AccountId, era_index: EraIndex) -> Option<MerkleProof>;
        fn verify_rewards_merkle_proof(merkle_proof: MerkleProof) -> bool;
    }
}

Where:

• generate_rewards_merkle_proof: generates a merkle proof for a given account_id and era_index. If the account_id was not rewarded in that era or was not present in the validator set for some reason, it returns None.
• verify_rewards_merkle_proof: verifies a merkle proof (that could be previously generated by calling generate_rewards_merkle_proof).

[github-actions]

Coverage Report

(master)

@@                   Coverage Diff                   @@
##           master   agustin-map-rewards      +/-   ##
=======================================================
+ Coverage   64.56%                64.73%   +0.17%     
+ Files         320                   323       +3     
+ Lines       55422                 55578     +156     
=======================================================
+ Hits        35781                 35974     +193     
- Misses      19641                 19604      -37     

Files Changed	Coverage
/pallets/external-validators/src/lib.rs	91.07% (+0.36%)	✅
/pallets/external-validators-rewards/src/lib.rs	89.58% (+7.12%)	✅
/primitives/bridge/src/custom_send_message.rs	85.71% (+85.71%)	✅
/primitives/bridge/src/lib.rs	58.72% (+58.72%)	✅
/primitives/traits/src/lib.rs	63.11% (-2.46%)	❗
/solo-chains/runtime/dancelight/src/lib.rs	66.91% (+0.70%)	✅

Coverage generated Tue Dec 10 13:04:20 UTC 2024

[girazoki]

minor comments, the rest looks good to me