Fix docs functionsphp

[prab18hat]

This pull request improves the inline documentation for the wp_parse_id_list() function in [functions.php]

Expanded the PHPDoc block to clearly specify accepted parameter types (int|string|array) and the return value (int[] array of unique, positive integers).
The updated documentation follows WordPress coding standards and helps developers better understand the function’s usage and output.
No code logic was changed—only the documentation was enhanced for clarity and maintainability.

https://core.trac.wordpress.org/ticket/63900

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