Added basic entity scripts

scripts/CSharp/GameEntity/LoadSave/EntityLoadSaveUtil.cs

@@ -0,0 +1,32 @@
+using Newtonsoft.Json.Linq;
+
+namespace Babushka.scripts.CSharp.GameEntity.LoadSave;
+
+public static class EntityLoadSaveUtil
+{
+    private static void AssertTokenType(this JObject json, string key, JTokenType type)
+    {
+        var token = json[key];
+        if (token == null) throw new MalformedJsonException(json, key, "does not exist");
+        if (!token.HasValues) throw new MalformedJsonException(json, key, "has no value");
+        if (token.Type != type) throw new MalformedJsonException(json, key, $"is not of type {type}");
+    }
+
+    public static long GetLongValue(this JObject json, string key)
+    {
+        AssertTokenType(json, key, JTokenType.Integer);
+        return json.Value<long>(key);
+    }
+    
+    public static float GetFloatValue(this JObject json, string key)
+    {
+        AssertTokenType(json, key, JTokenType.Float);
+        return json.Value<float>(key);
+    }
+    
+    public static string GetStringValue(this JObject json, string key)
+    {
+        AssertTokenType(json, key, JTokenType.String);
+        return json.Value<string>(key)!;
+    }
+}