Improved cache control

[giuscris]

This pull request updates the page response caching logic in PageController.php to improve cache accuracy and control. The main changes ensure that error pages are never cached, cache headers are generated based on the rendered content, and only cache GET/HEAD requests without query parameters. These improvements help prevent serving outdated or incorrect content.

Caching logic improvements:

• Error pages are now explicitly excluded from being cached by adding a check for !$page->isErrorPage() to the $cacheable condition.
• Cache headers (ETag and Last-Modified) are now generated using the rendered page content and its last modified time, instead of the content file path, for more accurate cache validation.
• The cache save operation now uses an optional cache time from the page configuration ($page->get('cache.time', null)), allowing for configurable cache durations.

Request cacheability refinement:

• Requests with query parameters are now excluded from caching by updating isRequestCacheable() to require an empty query string.

[Copilot]

Pull Request Overview

This PR improves page caching logic in the PageController by refactoring cache validation, fixing a typo, and adding additional caching constraints.

• Restructured the caching logic to separate cache retrieval from content generation
• Changed ETag generation to use rendered content instead of file path for better cache validation
• Added checks to prevent caching pages with query parameters and error pages

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