Optimize the reading of Transaction ID upon serialization

- The Transaction ID on events won't be calculated multiple times in cases where the same instance is serialized twice.
- Related to #269

Author: sondreb

src/Blockcore/Connection/Broadcasting/BroadcastTransactionStateChanedEntry.cs

@@ -10,10 +10,18 @@ public class BroadcastTransactionStateChanedEntry
         [JsonIgnore] // The "Transaction" cannot serialize for Web Socket.
         public Transaction Transaction { get; }
 
+        private string transactionId;
+
         /// <summary>
         /// Makes the transaction ID available for Web Socket consumers.
         /// </summary>
-        public string TransactionId { get { return this.Transaction.ToString(); } }
+        public string TransactionId
+        {
+            get
+            {
+                return this.transactionId ??= this.Transaction.ToString();
+            }
+        }
 
         [JsonConverter(typeof(StringEnumConverter))]
         public TransactionBroadcastState TransactionBroadcastState { get; set; }

src/Blockcore/EventBus/CoreEvents/TransactionReceived.cs

@@ -14,10 +14,18 @@ public class TransactionReceived : EventBase
         [JsonIgnore] // The "Transaction" cannot serialize for Web Socket.
         public Transaction ReceivedTransaction { get; }
 
+        private string transactionId;
+
         /// <summary>
         /// Makes the transaction ID available for Web Socket consumers.
         /// </summary>
-        public string TransactionId { get { return this.ReceivedTransaction.ToString(); } }
+        public string TransactionId
+        {
+            get
+            {
+                return this.transactionId ??= this.ReceivedTransaction.ToString();
+            }
+        }
 
         public TransactionReceived(Transaction receivedTransaction)
         {

src/Features/Blockcore.Features.Wallet/Events/TransactionFound.cs

@@ -17,10 +17,18 @@ public class TransactionFound : EventBase
         [JsonIgnore] // The "Transaction" cannot serialize for Web Socket.
         public Transaction FoundTransaction { get; }
 
+        private string transactionId;
+
         /// <summary>
         /// Makes the transaction ID available for Web Socket consumers.
         /// </summary>
-        public string TransactionId { get { return this.FoundTransaction.ToString(); } }
+        public string TransactionId
+        {
+            get
+            {
+                return this.transactionId ??= this.FoundTransaction.ToString();
+            }
+        }
 
         public TransactionFound(Transaction foundTransaction)
         {