Make package private class final

Allow no instances of some internal classes

src/main/java/org/apache/commons/csv/Constants.java

@@ -81,4 +81,9 @@ final class Constants {
 
     static final String[] EMPTY_STRING_ARRAY = {};
 
+    /** No instances. */
+    private Constants() {
+        // noop
+    }
+
 }

src/main/java/org/apache/commons/csv/IOUtils.java

@@ -23,7 +23,7 @@ import java.nio.Buffer;
 import java.nio.CharBuffer;
 
 /** Copied from Apache Commons IO. */
-class IOUtils {
+final class IOUtils {
 
     /**
      * <p>
@@ -137,4 +137,9 @@ class IOUtils {
         return count;
     }
 
+    /** No instances. */
+    private IOUtils() {
+        // Noop
+    }
+
 }