change store::on_gossip_attestation to take a ref to signed attestations

[d4m014]

Closes #271

This pr changes on_gossip_attestation in both store.rs and lib.rs to accept &SignedAttestation instead of taking ownership to avoid an unnecessary clone at the call site when self-delivering attestations to gossip_signatures, since only the inner data field (a small AttestationData) needs to be cloned to construct the Attestation.

[greptile-apps]

Greptile Summary

This PR changes store::on_gossip_attestation (and the BlockChainServer wrapper) to accept &SignedAttestation instead of consuming ownership, eliminating an unnecessary .clone() of the full SignedAttestation (including a 3112-byte XMSS signature) at the self-delivery call site. Only the small AttestationData field is now cloned inside the function where it is needed.

Confidence Score: 5/5

• Safe to merge — purely a refactoring that eliminates an unnecessary clone with no functional change.
• All changes are mechanical signature updates with no behavioral differences. The only trade-off (one additional cheap AttestationData clone inside the function) is clearly acceptable compared to the eliminated 3112-byte XMSS signature clone at the call site. No P0 or P1 findings.
• No files require special attention.

Important Files Changed

Filename	Overview
crates/blockchain/src/store.rs	Signature of on_gossip_attestation changed from owned SignedAttestation to &SignedAttestation; internal data field now cloned (cheap AttestationData clone) instead of moved. Logic is unchanged.
crates/blockchain/src/lib.rs	Both the BlockChainServer::on_gossip_attestation wrapper and its two call sites updated to pass &SignedAttestation; the expensive .clone() on the self-delivery path is now removed.

Sequence Diagram

sequenceDiagram
    participant P2P as P2P Gossip
    participant H as NewAttestation Handler
    participant BC as BlockChainServer
    participant Store as store on_gossip_attestation

    P2P->>H: "NewAttestation { attestation }"
    H->>BC: "on_gossip_attestation(&msg.attestation)"
    BC->>Store: "on_gossip_attestation(store, &signed_attestation)"
    Note over Store: "clone only AttestationData (small), decode sig bytes from ref"
    Store-->>BC: "Ok(()) / Err(StoreError)"

    Note over BC: "Self-delivery path (is_aggregator only)"
    BC->>Store: "on_gossip_attestation(store, &signed_attestation)"
    Note over Store: "Before: signed_attestation.clone() — 3112-byte XMSS sig copied. Now: borrow only, no large clone"
    Store-->>BC: "Ok(()) / Err(StoreError)"

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_{Reviews (1): Last reviewed commit: "Merge branch 'main' into refactor/gossip..." | Re-trigger Greptile}

[MegaRedHand]

LGTM