Added texture cache and sprite origins.

AlientAttack.MonoGame/Textures/TextureCache.cs

@@ -0,0 +1,26 @@
+using Microsoft.Xna.Framework.Content;
+using Microsoft.Xna.Framework.Graphics;
+using System.Collections.Generic;
+
+namespace AlienAttack.MonoGame.Textures;
+
+public sealed class TextureCache
+{
+    private readonly Dictionary<string, Texture2D> _cache = [];
+    private ContentManager _content = default!;
+
+    public void Initialize(ContentManager content) => _content = content;
+
+    public Texture2D Get(string assetName)
+    {
+        if (_cache.TryGetValue(assetName, out var texture))
+            return texture;
+
+        texture = _content.Load<Texture2D>(assetName);
+        _cache[assetName] = texture;
+
+        return texture;
+    }
+
+    public void Clear() => _cache.Clear();
+}