Add metrics for engine_getBlobsV1

src/Nethermind/Nethermind.Merge.Plugin/Handlers/GetBlobsHandler.cs

@@ -26,11 +26,19 @@ public Task<ResultWrapper<GetBlobsV1Result>> HandleAsync(byte[][] request)
 
     private IEnumerable<BlobAndProofV1?> GetBlobsAndProofs(byte[][] request)
     {
+        Metrics.NumberOfRequestedBlobs += request.Length;
+
         foreach (byte[] requestedBlobVersionedHash in request)
         {
-            yield return txPool.TryGetBlobAndProof(requestedBlobVersionedHash, out byte[]? blob, out byte[]? proof)
-                ? new BlobAndProofV1(blob, proof)
-                : null;
+            if (txPool.TryGetBlobAndProof(requestedBlobVersionedHash, out byte[]? blob, out byte[]? proof))
+            {
+                Metrics.NumberOfSentBlobs++;
+                yield return new BlobAndProofV1(blob, proof);
+            }
+            else
+            {
+                yield return null;
+            }
         }
     }
 }

src/Nethermind/Nethermind.Merge.Plugin/Metrics.cs

@@ -23,5 +23,13 @@ public static class Metrics
         [GaugeMetric]
         [Description("Number of Transactions included in the Last GetPayload Request")]
         public static int NumberOfTransactionsInGetPayload { get; set; }
+
+        [GaugeMetric]
+        [Description("Number of Blobs requested by engine_getBlobsV1")]
+        public static int NumberOfRequestedBlobs { get; set; }
+
+        [GaugeMetric]
+        [Description("Number of Blobs sent by engine_getBlobsV1")]
+        public static int NumberOfSentBlobs { get; set; }
     }
 }