[php-src] Issue #21568: uasort() with 'strnatcasecmp' acts weird

Issue: https://github.com/php/php-src/issues/21568
Author: staabm

### Description

we are in the process of covering the handling of `uasort` when using with `strnatcasecmp` and found a few things which we are not able to make sense of. I also looked thru the docs and did not find something which explained what we see.

the proble occur arround strict-types and `Stringable` vs. `string` territory.

especially interessting is that `strnatcasecmp` when invoked directly is happy with the given input, while using `strnatcasecmp` as callback via `uasort` errors. results vary with strict-types 0/1.

see
- https://3v4l.org/XgFEm#v8.3.30 (no error without declare)
- https://3v4l.org/slZeW#v8.3.30 (strnatcasecmp error with declare strict=1)
- https://3v4l.org/TdBcf#v8.3.30 (uasort doesn't error with declare strict=1)
- https://3v4l.org/AAlUE#v8.3.30 (uasort via arrow-fn using strnatcasecmp()) 

so our questions mainly are
- is all this expected behaviour?
- can someone share some insights so we can properly reflect php-src runtime behaviour in PHPStan?

thank you

### PHP Version

```plain
PHP 8.3.x
```

### Operating System

_No response_