refactor: port partial occlusion to Java

Keep the Scala trait helper so reference-compiled implementations remain linkable.

src/test/java/codechicken/multipart/PartialOcclusionCharacterizationTest.java

@@ -64,6 +64,13 @@ class PartialOcclusionCharacterizationTest {
         assertTrue(test.apply());
     }
 
+    @Test
+    void javaInterfaceDefaultsToRequiredVisibility() {
+        JPartialOcclusion part = Collections::emptyList;
+
+        assertFalse(part.allowCompleteOcclusion());
+    }
+
     @Test
     void fullyOverlappingPartsLoseTheirVisibleVoxel() {
         PartialOcclusionTest test = new PartialOcclusionTest(2);