Merge pull request #43 from boesing/bugfix/invalid-return-type-count

bugfix: implement `Countable::count` to provide `0|positive-int` as return type

Author: boesing

src/ArrayInterface.php

@@ -55,4 +55,9 @@ public function allSatisfy(callable $callback): bool;
      * @psalm-param callable(TValue):bool $callback
      */
     public function exists(callable $callback): bool;
+
+    /**
+     * @return 0|positive-int
+     */
+    public function count(): int;
 }