fix CallbackIterator to return mixed, as it can be overwritten with a callback

api/src/Db/CallbackIterator.php

@@ -134,9 +134,9 @@ class CallbackIterator implements \Iterator
 	/**
 	 * Return the key of the current element
 	 *
-	 * @return int
+	 * @return mixed
 	 */
-	public function key(): int
+	public function key(): mixed
 	{
 		if (is_a($this->rs,'iterator'))
 		{

doc/fix-8.1-depricated-interfaces-return-vals.php

@@ -31,7 +31,7 @@ $interfaces = [
 		'valid' => 'bool',
 	],
 	'IteratorAggregate' => [
-		'getIterator' => 'Traversable',
+		'getIterator' => '\Traversable',
 	],
 	'ArrayAccess' => [
 		'offsetExists' => 'bool',