feat(engine/ssz): add target_gas_limit to PayloadAttributesV4 wire

src/Nethermind/Nethermind.Merge.Plugin.Test/SszRest/SszCodecTests.cs

@@ -533,6 +533,7 @@ public void DecodeFcuV3Request_spec_layout_roundtrips_parent_beacon_block_root()
     public void DecodeFcuV4Request_spec_layout_roundtrips_parent_beacon_block_root_and_slot_number()
     {
         ulong expectedSlot = 0xAABBCCDD_11223344UL;
+        ulong expectedTargetGasLimit = 0x0123456789ABCDEFUL;
 
         ForkchoiceUpdatedRequestWire wire = new()
         {
@@ -552,6 +553,7 @@ public void DecodeFcuV4Request_spec_layout_roundtrips_parent_beacon_block_root_a
                     Withdrawals = [],
                     ParentBeaconBlockRoot = TestItem.KeccakE,
                     SlotNumber = expectedSlot,
+                    TargetGasLimit = expectedTargetGasLimit,
                 }
             ]
         };
@@ -569,6 +571,8 @@ public void DecodeFcuV4Request_spec_layout_roundtrips_parent_beacon_block_root_a
             "parent_beacon_block_root must round-trip in V4 as a fixed Bytes32");
         attrs.SlotNumber.Should().Be(expectedSlot,
             "slot_number must be decoded from the fixed uint64 that follows parent_beacon_block_root");
+        attrs.TargetGasLimit.Should().Be((long)expectedTargetGasLimit,
+            "target_gas_limit must be decoded from the fixed uint64 that follows slot_number");
         attrs.SuggestedFeeRecipient.Should().Be(TestItem.AddressB);
     }
 

src/Nethermind/Nethermind.Merge.Plugin/SszRest/SszCodec.cs

@@ -288,22 +288,25 @@ internal static PayloadAttributes PayloadAttributesFromWire(PayloadAttributesWir
         BuildPayloadAttributes(pa.Timestamp, pa.PrevRandao, pa.SuggestedFeeRecipient,
             withdrawals: pa.Withdrawals.ToDomain(),
             parentBeaconBlockRoot: pa.ParentBeaconBlockRoot,
-            slotNumber: pa.SlotNumber);
+            slotNumber: pa.SlotNumber,
+            targetGasLimit: (long)pa.TargetGasLimit);
 
     private static PayloadAttributes BuildPayloadAttributes(
         ulong timestamp,
         Hash256 prevRandao,
         Address suggestedFeeRecipient,
         Withdrawal[]? withdrawals = null,
         Hash256? parentBeaconBlockRoot = null,
-        ulong? slotNumber = null) => new()
+        ulong? slotNumber = null,
+        long? targetGasLimit = null) => new()
         {
             Timestamp = timestamp,
             PrevRandao = prevRandao,
             SuggestedFeeRecipient = suggestedFeeRecipient,
             Withdrawals = withdrawals,
             ParentBeaconBlockRoot = parentBeaconBlockRoot,
-            SlotNumber = slotNumber
+            SlotNumber = slotNumber,
+            TargetGasLimit = targetGasLimit
         };
 
 }

src/Nethermind/Nethermind.Merge.Plugin/SszRest/SszWireTypes.cs

@@ -80,6 +80,7 @@ public partial struct PayloadAttributesWire
     [SszList(16)] public SszWithdrawal[]? Withdrawals { get; set; }
     public Hash256 ParentBeaconBlockRoot { get; set; }
     public ulong SlotNumber { get; set; }
+    public ulong TargetGasLimit { get; set; }
 }
 
 [SszContainer]