Fix Javadoc warnings due to Java 21 update (+ some other warnings)

The default implicit constructor must also have a doc comment, so I have to make it explicit and either properly restrict the visibility of the constructor, or actually document it.

pandalib-bungee-permissions/src/main/java/fr/pandacube/lib/bungee/permissions/PandalibBungeePermissions.java

@@ -25,7 +25,6 @@ import java.util.function.Function;
  */
 public class PandalibBungeePermissions implements Listener {
 
-
     /**
      * Registers event listener to redirect permission checks to {@code pandalib-permissions}.
      * @param bungeePlugin a BungeeCord plugin.
@@ -35,6 +34,8 @@ public class PandalibBungeePermissions implements Listener {
     }
 
 
+    private PandalibBungeePermissions() {}
+
     /**
      * Event handler called when a plugin asks if a player has a permission.
      * @param event the permission check event.