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-chat/src/main/java/fr/pandacube/lib/chat/ChatStatic.java

@@ -679,5 +679,10 @@ public abstract class ChatStatic {
         return builder.style(c.style()).append(c.children());
     }
 
+    /**
+     * Creates a new {@link ChatStatic} instance.
+     */
+    protected ChatStatic() {}
+
 
 }