Add interface to allow receiving lifecycle callbacks on ObjectDevices.

src/main/java/li/cil/oc2/api/bus/device/object/LifecycleAwareDevice.java

@@ -0,0 +1,33 @@
+package li.cil.oc2.api.bus.device.object;
+
+import li.cil.oc2.api.bus.device.rpc.RPCDevice;
+import net.minecraft.world.entity.Entity;
+import net.minecraft.world.level.block.entity.BlockEntity;
+
+/***
+ * This interface is used to receive life-cycle callbacks on targets of an {@link ObjectDevice}.
+ * <p>
+ * In particular, this also includes {@link BlockEntity}s and {@link Entity}s providing {@link Callback}s.
+ */
+public interface LifecycleAwareDevice {
+    /**
+     * This method corresponds to {@link RPCDevice#mount()}. It is called when the device is initialized, either
+     * because its virtual machine starts running, or because it is added to a running virtual machine.
+     */
+    default void onDeviceMounted() {
+    }
+
+    /**
+     * This method corresponds to {@link RPCDevice#unmount()}. It is called when the device is disposed, either
+     * because its virtual machine stops running, or because it is removed from a running virtual machine.
+     */
+    default void onDeviceUnmounted() {
+    }
+
+    /**
+     * This method corresponds to {@link RPCDevice#suspend()}. It is called when its virtual machine is suspended,
+     * either due to the containing chunk being unloaded, or the containing world being unloaded.
+     */
+    default void onDeviceSuspended() {
+    }
+}

src/main/java/li/cil/oc2/api/bus/device/object/ObjectDevice.java

@@ -86,6 +86,27 @@ public final class ObjectDevice implements RPCDevice {
         return methods;
     }
 
+    @Override
+    public void mount() {
+        if (object instanceof LifecycleAwareDevice device) {
+            device.onDeviceMounted();
+        }
+    }
+
+    @Override
+    public void unmount() {
+        if (object instanceof LifecycleAwareDevice device) {
+            device.onDeviceUnmounted();
+        }
+    }
+
+    @Override
+    public void suspend() {
+        if (object instanceof LifecycleAwareDevice device) {
+            device.onDeviceSuspended();
+        }
+    }
+
     @Override
     public boolean equals(@Nullable final Object o) {
         if (this == o) return true;