create a convenience method on the header class

src/NATS.Client.Core/NatsHeaders.cs

@@ -294,6 +294,16 @@ public void CopyTo(KeyValuePair<string, StringValues>[] array, int arrayIndex)
         }
     }
 
+    /// <summary>
+    /// Returns the bytes length of the header
+    /// </summary>
+    /// <param name="headerWriter">an instance of headerWriter</param>
+    /// <returns>bytes length of th header</returns>
+    public long GetBytesLength(HeaderWriter headerWriter)
+    {
+        return headerWriter.GetBytesLength(this);
+    }
+
     /// <summary>
     /// Removes the given item from the the collection.
     /// </summary>

tests/NATS.Client.CoreUnit.Tests/NatsHeaderTest.cs

@@ -207,7 +207,7 @@ public void GetBytesLengthTest()
             ["key"] = "a-long-header-value",
         };
         var writer = new HeaderWriter(Encoding.UTF8);
-        var bytesLength = writer.GetBytesLength(headers);
+        var bytesLength = headers.GetBytesLength(writer);
 
         var text = "NATS/1.0\r\nk1: v1\r\nk2: v2-0\r\nk2: v2-1\r\na-long-header-key: value\r\nkey: a-long-header-value\r\n\r\n";
         var expected = new ReadOnlySequence<byte>(Encoding.UTF8.GetBytes(text));