Added SZ singleton and services

SzCli/Program.cs

@@ -1,12 +1,13 @@
 using System;
 using SzCore;
+using SzCore.Defaults;
 
 namespace SzCli;
 
 public class Program
 {
-    private static readonly ISzFileManager _fileManager = new LocalFileManager();
-    private static readonly ISzLogger _logger = new Logger(_fileManager);
+    private static readonly DefaultLocalFileManager _fileManager = new();
+    private static readonly Logger _logger = new(_fileManager);
     
     public static void Main(string[] args)
     {
@@ -24,6 +25,6 @@ public class Program
         var loadedDataset = parser.LoadDataset(dataset.Id);
         _logger.Log($"Successfully loaded dataset? {loadedDataset != null}. Id is {loadedDataset?.Id}");
         
-       _logger.Log(loadedDataset?.DataObjects["test"].Fields["value"].Value);
+       _logger.Log(loadedDataset?.DataObjects["test"].Fields["value"].Value ?? "Could not get value of test.value");
     }
 }