Add initial PHPStan config

[swissspidy]

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[github-actions]

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[codecov]

Codecov Report

❌ Patch coverage is 40.00000% with 6 lines in your changes missing coverage. Please review.

Files with missing lines	Patch %	Lines
inc/RestCommand.php	28.57%	5 Missing ⚠️
inc/Runner.php	66.66%	1 Missing ⚠️

📢 Thoughts on this report? Let us know!

[gemini-code-assist]

Code Review

This pull request introduces a PHPStan configuration and adds comprehensive PHPDoc type hints to improve static analysis. Key changes include refactoring the diff_items logic to be more explicit, replacing manual WP_INSTALLING constant checks with the wp_installing() function, and correcting the casing of the RestCommand class instantiation. A regression was identified in inc/RestCommand.php where removing the reference operator from the $assoc_args parameter in get_formatter prevents the Formatter from correctly modifying the arguments array as expected by WP-CLI.

[gemini-code-assist]

The $assoc_args parameter should be passed by reference. In WP-CLI, the Formatter class constructor expects a reference to the associative arguments array and may modify it (e.g., to remove formatting-specific flags so they aren't processed as data fields). By removing the reference here, get_formatter passes a local copy to the Formatter, which breaks the expected behavior where the Formatter can update the caller's arguments array.

protected function get_formatter( &$assoc_args ) {