Drastic website performance improvements

This Pull Request brings together a series of optimizations designed to significantly improve website performance by reducing database queries and accelerating page rendering.

The key changes are as follows:

Query and Prefetch Optimization: The code has been refactored to make the best use of Odoo's ORM prefetch mechanism. These changes allow for consolidating multiple data fetching queries into a single one, which improves overall efficiency and performance.

XML View Refactoring: The slow fields_get() method has been replaced with the _fields attribute in the template.layout view. This change is sufficient to check for a field's presence without overloading the system with unnecessary processing, resulting in a gain of approximately 8ms per page.

High-level Cache Introduction: A new cache has been added to the website.page model to store published pages. This cache can be controlled via overridable methods (_allow_to_use_cache, _allow_cache_insertion, _post_process_response_from_cache), allowing us to optimize rendering time for static or semi-static content.