Update to superstruct v0.4.1 (#2886)

## Proposed Changes

Update `superstruct` to bring in @realbigsean's fixes necessary for MEV-compatible private beacon block types (a la #2795).

The refactoring is due to another change in superstruct that allows partial getters to be auto-generated.

beacon_node/beacon_chain/src/beacon_chain.rs

@@ -1099,6 +1099,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
                     .message()
                     .body()
                     .execution_payload()
+                    .ok()
                     .map(|ep| ep.block_hash),
             })
         })
@@ -2602,7 +2603,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
         }
 
         // Register sync aggregate with validator monitor
-        if let Some(sync_aggregate) = block.body().sync_aggregate() {
+        if let Ok(sync_aggregate) = block.body().sync_aggregate() {
             // `SyncCommittee` for the sync_aggregate should correspond to the duty slot
             let duty_epoch = block.slot().epoch(T::EthSpec::slots_per_epoch());
             let sync_committee = self.sync_committee_at_epoch(duty_epoch)?;
@@ -2643,7 +2644,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
                 block.body().attestations().len() as f64,
             );
 
-            if let Some(sync_aggregate) = block.body().sync_aggregate() {
+            if let Ok(sync_aggregate) = block.body().sync_aggregate() {
                 metrics::set_gauge(
                     &metrics::BLOCK_SYNC_AGGREGATE_SET_BITS,
                     sync_aggregate.num_set_bits() as i64,
@@ -3241,6 +3242,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
             .message()
             .body()
             .execution_payload()
+            .ok()
             .map(|ep| ep.block_hash);
         let is_merge_transition_complete = is_merge_transition_complete(&new_head.beacon_state);
 
@@ -3528,6 +3530,7 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
             .message()
             .body()
             .execution_payload()
+            .ok()
             .map(|ep| ep.block_hash)
             .unwrap_or_else(Hash256::zero);
 

beacon_node/beacon_chain/src/execution_payload.rs

@@ -146,7 +146,7 @@ pub fn validate_execution_payload_for_gossip<T: BeaconChainTypes>(
     chain: &BeaconChain<T>,
 ) -> Result<(), BlockError<T::EthSpec>> {
     // Only apply this validation if this is a merge beacon block.
-    if let Some(execution_payload) = block.body().execution_payload() {
+    if let Ok(execution_payload) = block.body().execution_payload() {
         // This logic should match `is_execution_enabled`. We use only the execution block hash of
         // the parent here in order to avoid loading the parent state during gossip verification.
 
@@ -289,6 +289,7 @@ pub async fn prepare_execution_payload<T: BeaconChainTypes>(
                 .message()
                 .body()
                 .execution_payload()
+                .ok()
                 .map(|ep| ep.block_hash)
         };