Clean up publishing operations when they're removed from the pipeline (#714)

Author: SamCarlberg

core/src/main/java/edu/wpi/grip/core/operations/network/PublishAnnotatedOperation.java

@@ -162,4 +162,8 @@ protected Object get(Method accessor, Object instance) {
     }
   }
 
+  @Override
+  public void cleanUp() {
+    publisher.close();
+  }
 }