Check slashability of attestations in batches to avoid sequential bottleneck (#8516)

Closes:

- https://github.com/sigp/lighthouse/issues/1914


  Sign attestations prior to checking them against the slashing protection DB. This allows us to avoid the sequential DB checks which are observed in traces here:

- https://github.com/sigp/lighthouse/pull/8508#discussion_r2576686107


Co-Authored-By: Jimmy Chen <jchen.tc@gmail.com>

Co-Authored-By: Michael Sproul <michael@sigmaprime.io>

Co-Authored-By: Michael Sproul <michaelsproul@users.noreply.github.com>

validator_client/validator_store/src/lib.rs

@@ -19,9 +19,9 @@ pub enum Error<T> {
     Slashable(NotSafe),
     SameData,
     GreaterThanCurrentSlot { slot: Slot, current_slot: Slot },
-    GreaterThanCurrentEpoch { epoch: Epoch, current_epoch: Epoch },
     UnableToSignAttestation(AttestationError),
     SpecificError(T),
+    ExecutorError,
     Middleware(String),
 }
 
@@ -103,13 +103,24 @@ pub trait ValidatorStore: Send + Sync {
         current_slot: Slot,
     ) -> impl Future<Output = Result<SignedBlock<Self::E>, Error<Self::Error>>> + Send;
 
-    fn sign_attestation(
-        &self,
-        validator_pubkey: PublicKeyBytes,
-        validator_committee_position: usize,
-        attestation: &mut Attestation<Self::E>,
-        current_epoch: Epoch,
-    ) -> impl Future<Output = Result<(), Error<Self::Error>>> + Send;
+    /// Sign a batch of `attestations` and apply slashing protection to them.
+    ///
+    /// Only successfully signed attestations that pass slashing protection are returned, along with
+    /// the validator index of the signer. Eventually this will be replaced by `SingleAttestation`
+    /// use.
+    ///
+    /// Input:
+    ///
+    /// * Vec of (validator_index, pubkey, validator_committee_index, attestation).
+    ///
+    /// Output:
+    ///
+    /// * Vec of (validator_index, signed_attestation).
+    #[allow(clippy::type_complexity)]
+    fn sign_attestations(
+        self: &Arc<Self>,
+        attestations: Vec<(u64, PublicKeyBytes, usize, Attestation<Self::E>)>,
+    ) -> impl Future<Output = Result<Vec<(u64, Attestation<Self::E>)>, Error<Self::Error>>> + Send;
 
     fn sign_validator_registration_data(
         &self,