feat: make Sand/Snow opaque and register Sand/Snow/Water blocks

World/Blocks/SnowBlock.cs

@@ -0,0 +1,16 @@
+namespace VoxelEngine.World.Blocks;
+
+public class SnowBlock : IBlock
+{
+    public ushort Id => 5;
+    public string Name => "Snow Block";
+    public bool IsOpaque => true;
+    public bool IsSolid => true;
+
+    public TileCoord GetTextureTile(BlockFace face) => face switch
+    {
+        BlockFace.Top => new TileCoord(2, 0),
+        BlockFace.Bottom => new TileCoord(0, 0),
+        _ => new TileCoord(3, 0)
+    };
+}