fix: resolve composer dependency conflict breaking CI tests

The CI integration tests were failing because composer.lock was out of
sync with composer.json. The root cause was phpcompatibility/php-compatibility
using "dev-develop as 9.99.99" which requires PHPCS 4.x, conflicting with
automattic/vipwpcs ^3.0 which requires PHPCS 3.x.

Changes:
- Pin phpcompatibility/php-compatibility to stable ^9.3
- Regenerate composer.lock with compatible dependencies
- Add native type hints to properties flagged by updated coding standards

Author: josephfusco

plugins/hwp-previews/composer.json

@@ -42,7 +42,7 @@
 		"johnpbloch/wordpress-core": "^6.8",
 		"lucatume/wp-browser": "^3.5",
 		"mockery/mockery": "^1.6",
-		"phpcompatibility/php-compatibility": "dev-develop as 9.99.99",
+		"phpcompatibility/php-compatibility": "^9.3",
 		"phpcompatibility/phpcompatibility-wp": "^2.0",
 		"phpstan/phpstan-strict-rules": "^2.0",
 		"slevomat/coding-standard": "^8.0",