feat: add Chunk as a dense 16-cubed id array

VoxelEngine.Tests/ChunkTests.cs

@@ -0,0 +1,40 @@
+using VoxelEngine.World;
+using Xunit;
+
+namespace VoxelEngine.Tests;
+
+public class ChunkTests
+{
+    [Fact]
+    public void Size_Is16()
+    {
+        Assert.Equal(16, Chunk.Size);
+    }
+
+    [Fact]
+    public void NewChunk_IsAllAir()
+    {
+        var chunk = new Chunk();
+        Assert.Equal((ushort)0, chunk[0, 0, 0]);
+        Assert.Equal((ushort)0, chunk[15, 15, 15]);
+    }
+
+    [Fact]
+    public void Indexer_StoresAndReturnsId()
+    {
+        var chunk = new Chunk();
+        chunk[1, 2, 3] = 7;
+        Assert.Equal((ushort)7, chunk[1, 2, 3]);
+        Assert.Equal((ushort)0, chunk[3, 2, 1]);
+    }
+
+    [Theory]
+    [InlineData(0, 0, 0, true)]
+    [InlineData(15, 15, 15, true)]
+    [InlineData(-1, 0, 0, false)]
+    [InlineData(0, 16, 0, false)]
+    public void InBounds_ChecksCoordinates(int x, int y, int z, bool expected)
+    {
+        Assert.Equal(expected, Chunk.InBounds(x, y, z));
+    }
+}

World/Chunk.cs

@@ -0,0 +1,19 @@
+namespace VoxelEngine.World;
+
+public sealed class Chunk
+{
+    public const int Size = 16;
+
+    private readonly ushort[] _ids = new ushort[Size * Size * Size];
+
+    public ushort this[int x, int y, int z]
+    {
+        get => _ids[Index(x, y, z)];
+        set => _ids[Index(x, y, z)] = value;
+    }
+
+    public static bool InBounds(int x, int y, int z) =>
+        x >= 0 && x < Size && y >= 0 && y < Size && z >= 0 && z < Size;
+
+    private static int Index(int x, int y, int z) => (x * Size + y) * Size + z;
+}