Refactor JSON serialization to use MemoryStream

Replaced StringWriter with MemoryStream and StreamWriter for JSON serialization to improve efficiency. JsonWriter is now initialized with StreamWriter. Adjusted indentation levels in ProcessStructure and ProcessMembers methods. Final request content is now obtained as a byte array from MemoryStream.

generator/ServiceClientGeneratorLib/Generators/Marshallers/JsonRPCRequestMarshaller.tt

@@ -93,32 +93,35 @@ namespace <#=this.Config.Namespace #>.Model.Internal.MarshallTransformations
 	if (this.Operation.RequestHasBodyMembers || shouldMarshallPayload)
 	{
 #>
-			using (StringWriter stringWriter = new StringWriter(CultureInfo.InvariantCulture))
-			{
-				JsonWriter writer = new JsonWriter(stringWriter);
-				writer.Validate = false;
+            using (MemoryStream memoryStream = new MemoryStream())
+            {
+                using (SreamWriter sreamWriter = new SreamWriter(memoryStream, null, -1, true))
+                {
+                    JsonWriter writer = new JsonWriter(sreamWriter);
+				    writer.Validate = false;
 <#		
 		if (shouldMarshallPayload)
 		{
 #>
-				var context = new JsonMarshallerContext(request, writer);
+				    var context = new JsonMarshallerContext(request, writer);
 <#		
-			ProcessStructure(0, "publicRequest." + payload.PropertyName, payload.Shape);
+			ProcessStructure(1, "publicRequest." + payload.PropertyName, payload.Shape);
 		}
 		else
 		{
 #>
-				writer.WriteObjectStart();
-				var context = new JsonMarshallerContext(request, writer);
+				    writer.WriteObjectStart();
+				    var context = new JsonMarshallerContext(request, writer);
 <#		
-				ProcessMembers(1, "publicRequest", this.Operation.RequestBodyMembers);
+				ProcessMembers(2, "publicRequest", this.Operation.RequestBodyMembers);
 #>
-				writer.WriteObjectEnd();
+				    writer.WriteObjectEnd();
 <#
 		}
 #>
-				string snippet = stringWriter.ToString();
-				request.Content = System.Text.Encoding.UTF8.GetBytes(snippet);
+                }
+
+                request.Content = memoryStream.ToArray();
 <#
 					GenerateRequestChecksumHandling(this.Operation, "snippet");
 #>