Update Slice operation

src/Collection.php

@@ -609,7 +609,7 @@ public function skip(int ...$counts): CollectionInterface
         return $this->run(new Skip(...$counts));
     }
 
-    public function slice(int $offset, ?int $length = null): CollectionInterface
+    public function slice(int $offset, int $length = -1): CollectionInterface
     {
         return $this->run(new Slice($offset, $length));
     }

src/Contract/Operation/Sliceable.php

@@ -16,9 +16,7 @@ interface Sliceable
     /**
      * Get a slice of a collection.
      *
-     * @param ?int $length
-     *
      * @psalm-return \loophp\collection\Contract\Collection<TKey, T>
      */
-    public function slice(int $offset, ?int $length = null): Collection;
+    public function slice(int $offset, int $length = -1): Collection;
 }

src/Operation/Slice.php

@@ -17,7 +17,7 @@
  */
 final class Slice extends AbstractOperation implements Operation
 {
-    public function __construct(int $offset, ?int $length = null)
+    public function __construct(int $offset, int $length = -1)
     {
         $this->storage = [
             'offset' => $offset,
@@ -33,10 +33,10 @@ public function __invoke(): Closure
              *
              * @psalm-return Generator<TKey, T>
              */
-            static function (Iterator $iterator, int $offset, ?int $length): Generator {
+            static function (Iterator $iterator, int $offset, int $length): Generator {
                 $skip = (new Run(new Skip($offset)))($iterator);
 
-                if (null === $length) {
+                if (-1 === $length) {
                     return yield from $skip;
                 }