Adding nix shell and reworking some parser/local file manager stuff

SzCli/LocalFileManager.cs

@@ -1,4 +1,6 @@
+using System.Reflection.Metadata;
 using SzLib;
+using SzLib.DataObjects;
 
 namespace SzCli;
 
@@ -18,10 +20,16 @@ public class LocalFileManager : ISzFileManager
         }
     }
 
+    public string DatasetsPath => Path.Combine(DataPath, "datasets");
+
     public bool SaveFile(string path, string fileContent)
     {
         try
         {
+            var dir = Path.GetDirectoryName(path);
+            if (dir is null) return false;
+            Directory.CreateDirectory(dir);
+            
             File.WriteAllText(path, fileContent);
             return true;
         }
@@ -31,4 +39,17 @@ public class LocalFileManager : ISzFileManager
             return false;
         }
     }
-}
+
+    public string? LoadFile(string path)
+    {
+        try
+        {
+            return File.ReadAllText(path);
+        }
+        catch (Exception e)
+        {
+            Console.WriteLine($"Error saving file: {e.Message}");
+            return null; 
+        }
+    }
+}