Rust clippy 1.87 lint fixes (#7471)

Fix clippy lints for `rustc` 1.87


  clippy complains about `BeaconChainError` being too large. I went on a bit of a boxing spree because of this. We may instead want to `Box` some of the `BeaconChainError` variants?

consensus/state_processing/src/per_epoch_processing/altair.rs

@@ -84,7 +84,7 @@ pub fn process_epoch<E: EthSpec>(
     Ok(EpochProcessingSummary::Altair {
         progressive_balances: current_epoch_progressive_balances,
         current_epoch_total_active_balance,
-        participation: participation_summary,
+        participation: participation_summary.into(),
         sync_committee,
     })
 }

consensus/state_processing/src/per_epoch_processing/epoch_processing_summary.rs

@@ -17,7 +17,7 @@ pub enum EpochProcessingSummary<E: EthSpec> {
     Altair {
         progressive_balances: ProgressiveBalancesCache,
         current_epoch_total_active_balance: u64,
-        participation: ParticipationEpochSummary<E>,
+        participation: Box<ParticipationEpochSummary<E>>,
         sync_committee: Arc<SyncCommittee<E>>,
     },
 }