Move EventCharacteristic to the internal package

src/main/java/net/minecraftforge/eventbus/api/event/characteristic/Cancellable.java

@@ -6,6 +6,7 @@
 
 import net.minecraftforge.eventbus.api.bus.CancellableEventBus;
 import net.minecraftforge.eventbus.internal.Event;
+import net.minecraftforge.eventbus.internal.EventCharacteristic;
 
 /**
  * A cancellable event returns {@code true} from {@link CancellableEventBus#post(Event)} if it was cancelled.

src/main/java/net/minecraftforge/eventbus/api/event/characteristic/MonitorAware.java

@@ -5,6 +5,7 @@
 package net.minecraftforge.eventbus.api.event.characteristic;
 
 import net.minecraftforge.eventbus.api.event.MutableEvent;
+import net.minecraftforge.eventbus.internal.EventCharacteristic;
 import net.minecraftforge.eventbus.internal.MutableEventInternals;
 
 /**

src/main/java/net/minecraftforge/eventbus/api/event/characteristic/SelfDestructing.java

@@ -6,6 +6,7 @@
 
 import net.minecraftforge.eventbus.api.bus.EventBus;
 import net.minecraftforge.eventbus.internal.AbstractEventBusImpl;
+import net.minecraftforge.eventbus.internal.EventCharacteristic;
 
 /**
  * A self-destructing event will {@link AbstractEventBusImpl#dispose() dispose} of its associated {@link EventBus}

src/main/java/net/minecraftforge/eventbus/api/event/characteristic/SelfPosting.java

@@ -6,6 +6,7 @@
 
 import net.minecraftforge.eventbus.api.bus.EventBus;
 import net.minecraftforge.eventbus.internal.Event;
+import net.minecraftforge.eventbus.internal.EventCharacteristic;
 
 /**
  * Experimental feature - may be removed, renamed or otherwise changed without notice.

src/main/java/net/minecraftforge/eventbus/internal/EventCharacteristic.java

@@ -0,0 +1,12 @@
+/*
+ * Copyright (c) Forge Development LLC
+ * SPDX-License-Identifier: LGPL-2.1-only
+ */
+package net.minecraftforge.eventbus.internal;
+
+import net.minecraftforge.eventbus.api.event.characteristic.Cancellable;
+import net.minecraftforge.eventbus.api.event.characteristic.MonitorAware;
+import net.minecraftforge.eventbus.api.event.characteristic.SelfDestructing;
+import net.minecraftforge.eventbus.api.event.characteristic.SelfPosting;
+
+public sealed interface EventCharacteristic permits Cancellable, MonitorAware, SelfDestructing, SelfPosting {}