Process transfers in parallel.

eth2/state_processing/src/per_block_processing.rs

@@ -442,8 +442,15 @@ pub fn process_transfers(
         transfers.len() as u64 <= spec.max_transfers,
         Invalid::MaxTransfersExceed
     );
+
+    transfers
+        .par_iter()
+        .enumerate()
+        .try_for_each(|(i, transfer)| {
+            verify_transfer(&state, transfer, spec).map_err(|e| e.into_with_index(i))
+        })?;
+
     for (i, transfer) in transfers.iter().enumerate() {
-        verify_transfer(&state, transfer, spec).map_err(|e| e.into_with_index(i))?;
         execute_transfer(state, transfer, spec).map_err(|e| e.into_with_index(i))?;
     }
 

eth2/types/src/test_utils/testing_transfer_builder.rs

@@ -9,7 +9,7 @@ impl TestingTransferBuilder {
     pub fn new(from: u64, to: u64, amount: u64, slot: Slot) -> Self {
         let keypair = Keypair::random();
 
-        let mut transfer = Transfer {
+        let transfer = Transfer {
             from,
             to,
             amount,