feat(world-gen): move cave ceiling and dark bands to new sea level (256)

VoxelEngine.Tests/ConfigurationTests.cs

@@ -70,8 +70,8 @@ public class ConfigurationTests
         Assert.Equal(3.5f,  c.WormMaxRadius);
 
         // Lighting (fog)
-        Assert.Equal(72f,   c.CaveDarkStartY);    // SeaLevel (64) + 8
-        Assert.Equal(32f,   c.CaveDarkEndY);      // SeaLevel (64) - 32
+        Assert.Equal(264f,  c.CaveDarkStartY);    // SeaLevel (256) + 8
+        Assert.Equal(224f,  c.CaveDarkEndY);      // SeaLevel (256) - 32
         Assert.Equal(0.15f, c.CaveMinBrightness);
     }
 
@@ -83,6 +83,6 @@ public class ConfigurationTests
         Assert.Equal(1, c.SurfaceShellSkirtBelow);
         Assert.Equal(0.7f, c.FogStartFraction);
         Assert.Equal(new OpenTK.Mathematics.Vector3(0.45f, 0.65f, 0.95f), c.SkyColor);
-        Assert.Equal(127, c.MinCaveY);
+        Assert.Equal(256, c.MinCaveY);
     }
 }