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-util/src/main/java/fr/pandacube/lib/util/EnumUtil.java

@@ -84,4 +84,6 @@ public class EnumUtil {
 		return RandomUtil.arrayElement(enumType.getEnumConstants());
 	}
 
+	private EnumUtil() {}
+
 }