Merge master into 3D terrain

- Resolve IrisTerrainNormalActuator by keeping master's primitive riverWaterSurfaceStream lookup and primarySurfaceLayerOrNull accessors while retaining the terrain column, span, layer surface and ceiling locals that write air through terrain3D gaps
- Resolve HydrologyFootprintCompiler by keeping the MaterializedSurface planned-surface record with terrain ownership beside master's package-private SurfaceRasterIndex, which retains its ownsTerrain override
- Resolve HydrologyCaveContainmentPlanner by dropping the nested RecordingCaveVoxelView, SurfaceObservations and ViewObservations types that master promoted to their own files
- Port the surface-observation ownership check into CaveSurfaceObservations so cached cave validations replay both height and ownership observations through Observation.matches
- Resolve PackExportClosureTest by keeping master's retirement of the source-text packager guard while retaining the snippet export tests, and restore the Files and Path imports those tests use
- Resolve IrisBiomeLayerSlopeSourceTest by folding the lower-ledge slope palette case into master's lockLayers parameterization
- Recapture the studio schema digest for the terrain3D biome property, its IrisTerrain3D definition, the terrain-3d snippet enumeration and the reworded upperDimensionCarving description, verified by reconstructing the previous digest from the stripped schema

probe/src/test/java/art/arcane/iris/probe/DimensionStackSuperflatProbeTest.java

@@ -4,6 +4,8 @@ import art.arcane.iris.engine.DimensionStackContext;
 import art.arcane.iris.engine.DimensionStackLayout;
 import art.arcane.iris.engine.framework.Engine;
 import art.arcane.iris.spi.PlatformBlockState;
+import art.arcane.iris.testsupport.IrisRuntimeState;
+import org.junit.AfterClass;
 import org.junit.Test;
 
 import java.io.File;
@@ -20,6 +22,11 @@ import static org.junit.Assert.assertNotNull;
 import static org.junit.Assert.assertTrue;
 
 public final class DimensionStackSuperflatProbeTest {
+    @AfterClass
+    public static void releaseProbeRuntime() {
+        IrisRuntimeState.reset();
+    }
+
     private static final long SEED = 1_337L;
     private static final long ALTERNATE_SEED = 8_675_309L;
     private static final int WORLD_HEIGHT = 128;

probe/src/test/java/art/arcane/iris/probe/StubPlatformStateTest.java

@@ -4,8 +4,11 @@ import art.arcane.iris.engine.decorator.IrisSpeleothems;
 import art.arcane.iris.engine.object.IrisObjectRotation;
 import art.arcane.iris.spi.IrisPlatforms;
 import art.arcane.iris.spi.PlatformBlockState;
+import art.arcane.iris.testsupport.PlatformLeakGuard;
 import art.arcane.iris.util.project.hunk.Hunk;
+import org.junit.AfterClass;
 import org.junit.BeforeClass;
+import org.junit.ClassRule;
 import org.junit.Test;
 
 import static org.junit.Assert.assertEquals;
@@ -14,13 +17,20 @@ import static org.junit.Assert.assertSame;
 import static org.junit.Assert.assertTrue;
 
 public final class StubPlatformStateTest {
+    @ClassRule
+    public static final PlatformLeakGuard LEAK_GUARD = PlatformLeakGuard.clean();
+
     @BeforeClass
     public static void bindPlatform() {
-        IrisPlatforms.unbind();
         IrisPlatforms.bind(new StubPlatform());
         StubPlatform.bindGenerationStateHandlers();
     }
 
+    @AfterClass
+    public static void unbindPlatform() {
+        IrisPlatforms.unbind();
+    }
+
     @Test
     public void rotatesFacingAxisAndConnectedFaces() {
         IrisObjectRotation rotation = IrisObjectRotation.of(0, 90, 0);