Feature request

I just spent a couple of hours on this, and PHPStan didn't save me. My code looks something like this:

/** @var array<array-key, mixed> */
$myArr = [ ... ];
$k = array_search('myneedle', $myArr, true);
...
unset($myArr[$k]);

The problem was that I was unsetting $myArr[0] when array_search() returned false. PHPStan also doesn't complain about $myArr[42.69]. I think anything but strings and integers should be disallowed as array offsets.