Add initial implementation of game mechanics and resources management

Scripts/Core/Effects/ModifyStatEffect.cs

@@ -0,0 +1,30 @@
+using Godot;
+
+namespace ParasiticGod.Scripts.Core.Effects;
+
+[GlobalClass]
+public partial class ModifyStatEffect : Effect
+{
+    public enum Stat { FaithPerFollower }
+    public enum Operation { Add, Multiply }
+    
+    [Export] public Stat TargetStat { get; set; }
+    [Export] public Operation Op { get; set; }
+    [Export] public double Value { get; set; }
+    
+    public override void Execute(GameState gameState)
+    {
+        if (TargetStat == Stat.FaithPerFollower)
+        {
+            switch (Op)
+            {
+                case Operation.Add:
+                    gameState.FaithPerFollower += Value;
+                    break;
+                case Operation.Multiply:
+                    gameState.FaithPerFollower *= Value;
+                    break;
+            }
+        }
+    }
+}