Compensate for PHP 8.1 backward compatibility issues

Author: andrewdalpino

src/Matrix.php

@@ -12,7 +12,7 @@
 use Tensor\Exceptions\DimensionalityMismatch;
 use Tensor\Exceptions\RuntimeException;
 use Tensor\Exceptions\NotImplemented;
-use Generator;
+use Traversable;
 
 use function count;
 use function is_float;
@@ -3435,7 +3435,7 @@ public function offsetGet($index) : Vector
      *
      * @return \Generator<int,\Tensor\Vector>
      */
-    public function getIterator() : Generator
+    public function getIterator() : Traversable
     {
         foreach ($this->a as $row) {
             yield Vector::quick($row);

src/Vector.php

@@ -6,6 +6,7 @@
 use Tensor\Exceptions\DimensionalityMismatch;
 use Tensor\Exceptions\RuntimeException;
 use ArrayIterator;
+use Traversable;
 
 use function count;
 use function is_float;
@@ -2303,6 +2304,7 @@ public function offsetUnset($index) : void
      * @throws \Tensor\Exceptions\InvalidArgumentException
      * @return float
      */
+    #[\ReturnTypeWillChange]
     public function offsetGet($index)
     {
         if (isset($this->a[$index])) {
@@ -2318,7 +2320,7 @@ public function offsetGet($index)
      *
      * @return \ArrayIterator<int,float>
      */
-    public function getIterator() : ArrayIterator
+    public function getIterator() : Traversable
     {
         return new ArrayIterator($this->a);
     }