Rework game over logic and game initialization

Zennysoft.Game.Ma/src/items/ItemDatabase.cs

@@ -1,4 +1,5 @@
 using Godot;
+using System;
 using System.Collections.Generic;
 using System.Collections.Immutable;
 using System.Linq;
@@ -6,11 +7,16 @@ using Zennysoft.Ma.Adapter;
 
 namespace Zennysoft.Game.Ma;
 
-public partial class ItemDatabase : Node
+public class ItemDatabase
 {
+  private static readonly Lazy<ItemDatabase> lazy =
+      new Lazy<ItemDatabase>(() => new ItemDatabase());
+
+  public static ItemDatabase Instance { get { return lazy.Value; } }
+
   public ImmutableList<InventoryItem> Items { get; set; }
 
-  public InventoryItem PickItem<T>(T itemToExclude = null)
+  public T PickItem<T>(T itemToExclude = null)
     where T : InventoryItem
   {
     var rng = new RandomNumberGenerator();
@@ -27,10 +33,10 @@ public partial class ItemDatabase : Node
     if (selectedItem is ThrowableItem throwableItem)
       throwableItem.SetCount(rng.RandiRange(throwableItem.Stats.MinimumCount, throwableItem.Stats.MaximumCount));
 
-    return selectedItem;
+    return (T)selectedItem;
   }
 
-  public ItemDatabase()
+  private ItemDatabase()
   {
     var database = new List<InventoryItem>();
     var armorResources = DirAccess.GetFilesAt("res://src/items/armor/resources/");