feat: add block model with IBlock flyweight and registry

World/Blocks/AirBlock.cs

@@ -0,0 +1,10 @@
+namespace VoxelEngine.World.Blocks;
+
+public sealed class AirBlock : IBlock
+{
+    public ushort Id => 0;
+    public string Name => "Air";
+    public bool IsOpaque => false;
+    public bool IsSolid => false;
+    public int GetTextureIndex(BlockFace face) => 0;
+}