Fix Withdrawal serialisation and check address change fork (#3789)

* Disallow address changes before Capella

* Quote u64s in Withdrawal serialisation

beacon_node/beacon_chain/src/beacon_chain.rs

@@ -2191,7 +2191,14 @@ impl<T: BeaconChainTypes> BeaconChain<T> {
     ) -> Result<ObservationOutcome<SignedBlsToExecutionChange, T::EthSpec>, Error> {
         #[cfg(feature = "withdrawals-processing")]
         {
+            let current_fork = self.spec.fork_name_at_slot::<T::EthSpec>(self.slot()?);
+            if let ForkName::Base | ForkName::Altair | ForkName::Merge = current_fork {
+                // Disallow BLS to execution changes prior to the Capella fork.
+                return Err(Error::BlsToExecutionChangeBadFork(current_fork));
+            }
+
             let wall_clock_state = self.wall_clock_state()?;
+
             Ok(self
                 .observed_bls_to_execution_changes
                 .lock()

beacon_node/beacon_chain/src/errors.rs

@@ -206,6 +206,7 @@ pub enum BeaconChainError {
     MissingPersistedForkChoice,
     CommitteePromiseFailed(oneshot_broadcast::Error),
     MaxCommitteePromises(usize),
+    BlsToExecutionChangeBadFork(ForkName),
 }
 
 easy_from_to!(SlotProcessingError, BeaconChainError);

consensus/types/src/withdrawal.rs

@@ -12,8 +12,10 @@ use tree_hash_derive::TreeHash;
 pub struct Withdrawal {
     #[serde(with = "eth2_serde_utils::quoted_u64")]
     pub index: u64,
+    #[serde(with = "eth2_serde_utils::quoted_u64")]
     pub validator_index: u64,
     pub address: Address,
+    #[serde(with = "eth2_serde_utils::quoted_u64")]
     pub amount: u64,
 }