Added shared update notices

- Iris joins shared Volmit update checks and reports
- The iris.update permission controls update visibility
- general.updateNotifications defaults to enabled
- Accepted settings changes reconfigure update checks
- Shutdown removes the settings listener and closes update checks
- Tests cover persisted opt-outs and notifier lifecycle

core/src/test/java/art/arcane/iris/configuration/IrisSettingsDefaultsTest.java

@@ -12,6 +12,16 @@ import static org.junit.Assert.assertTrue;
 import static org.junit.Assert.assertThrows;
 
 public class IrisSettingsDefaultsTest {
+    @Test
+    public void updateChecksDefaultOnAndPersistAnExplicitOptOut() {
+        assertTrue(IrisSettings.parseHotloadSnapshot("{}").getGeneral().isUpdateNotifications());
+        IrisSettings optedOut = IrisSettings.parseHotloadSnapshot(
+                "{\"general\":{\"updateNotifications\":false}}");
+        assertFalse(optedOut.getGeneral().isUpdateNotifications());
+        assertFalse(new Gson().fromJson(new Gson().toJson(optedOut), IrisSettings.class)
+                .getGeneral().isUpdateNotifications());
+    }
+
     @Test
     public void regionBudgetLeavesHeapForHydrologyAndServerChunks() {
         IrisSettings.IrisSettingsPregen settings = new IrisSettings.IrisSettingsPregen();