Fix: improve rejected pages config handling and nonce verification

[kraftbj]

Summary

Cherry-picks the still-relevant changes from closed PR #487 ("Improve wp-cache config functions"), adapted to the current codebase.

Originally proposed by @stodorovic in #487.

Changes to wp_cache_update_rejected_pages():

• Improved regex for config replacement: The regex now handles both single-quoted and double-quoted array keys in the config file ($wp_cache_pages['search'] and $wp_cache_pages["search"]), preventing stale entries when the quote style in the config doesn't match the hardcoded pattern.
• Inline nonce verification: Replaced reliance on the $valid_nonce global with a direct wp_verify_nonce() call, making the security check self-contained and explicit.
• Removed unnecessary global: Dropped the $valid_nonce global declaration since it is no longer used.

See #487

[Copilot]

Pull request overview

This PR updates how rejected page-type caching settings are persisted to the WP Super Cache config, improving config line matching and making nonce verification explicit within wp_cache_update_rejected_pages().

Changes:

• Updates wp_cache_update_rejected_pages() to verify the nonce inline via wp_verify_nonce() and removes the $valid_nonce global dependency.
• Enhances the config replacement regex so it matches both single-quoted and double-quoted $wp_cache_pages[...] keys when updating wp-cache-config.php.

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