refactor classes to be final

application/src/main/java/org/togetherjava/tjbot/features/moderation/history/MessageHistoryRoutine.java

@@ -19,7 +19,7 @@
 /**
  * Routine that deletes records from message_history post expiration hours.
  */
-public class MessageHistoryRoutine implements Routine {
+public final class MessageHistoryRoutine implements Routine {
     private static final Logger logger = LoggerFactory.getLogger(MessageHistoryRoutine.class);
     private static final int SCHEDULE_INTERVAL_SECONDS = 30;
     private static final int EXPIRATION_HOURS = 24;

application/src/main/java/org/togetherjava/tjbot/features/moderation/history/PurgeHistoryCommand.java

@@ -27,7 +27,7 @@
 
 import static org.togetherjava.tjbot.db.generated.Tables.MESSAGE_HISTORY;
 
-public class PurgeHistoryCommand extends SlashCommandAdapter {
+public final class PurgeHistoryCommand extends SlashCommandAdapter {
 
     private static final Logger logger = LoggerFactory.getLogger(PurgeHistoryCommand.class);
     private static final String USER_OPTION = "user";

application/src/main/java/org/togetherjava/tjbot/features/moderation/history/PurgeMessageListener.java

@@ -16,7 +16,7 @@
  * Listens for new message throughout the guild, then stores some metadata for each message in a
  * database.
  */
-public class PurgeMessageListener extends MessageReceiverAdapter {
+public final class PurgeMessageListener extends MessageReceiverAdapter {
     private static final Logger logger = LoggerFactory.getLogger(PurgeMessageListener.class);
     private static final int MESSAGES_RECORDS_LIMIT = 7500;
     static AtomicInteger recordsCounter = new AtomicInteger(0);