[attributes] Introduce attributes extensions

tweed5-core/src/main/java/de/siphalor/tweed5/core/api/extension/TweedExtension.java

@@ -15,6 +15,9 @@ public interface TweedExtension {
 	default void extensionsFinalized() {
 	}
 
+	default void initialize() {
+	}
+
 	default void initEntry(ConfigEntry<?> configEntry) {
 	}
 }

tweed5-core/src/main/java/de/siphalor/tweed5/core/impl/DefaultConfigContainer.java

@@ -217,6 +217,10 @@ public class DefaultConfigContainer<T> implements ConfigContainer<T> {
 	public void initialize() {
 		requireSetupPhase(ConfigContainerSetupPhase.TREE_ATTACHED);
 
+		for (TweedExtension extension : extensions()) {
+			extension.initialize();
+		}
+
 		assert rootEntry != null;
 		rootEntry.visitInOrder(entry -> {
 			for (TweedExtension extension : extensions()) {

tweed5-core/src/test/java/de/siphalor/tweed5/core/impl/sort/AcyclicGraphSorterTest.java

@@ -9,6 +9,13 @@ import static org.junit.jupiter.api.Assertions.*;
 
 class AcyclicGraphSorterTest {
 
+	@Test
+	void trivialSort() {
+		AcyclicGraphSorter sorter = new AcyclicGraphSorter(2);
+		sorter.addEdge(0, 1);
+		assertArrayEquals(new int[]{ 0, 1 }, assertDoesNotThrow(sorter::sort));
+	}
+
 	@Test
 	void sort1() {
 		AcyclicGraphSorter sorter = new AcyclicGraphSorter(4);
@@ -73,4 +80,4 @@ class AcyclicGraphSorterTest {
 		AcyclicGraphSorter.GraphCycleException exception = assertThrows(AcyclicGraphSorter.GraphCycleException.class, sorter::sort);
 		assertEquals(Arrays.asList(0, 1), exception.cycleIndeces());
 	}
-}
+}