This pull request introduces improvements to the handling of Chilean electronic document sequences, enforces stricter validation for certificate data, and modernizes string formatting throughout the codebase. The most significant changes focus on ensuring that document folio numbers are correctly managed in accordance with available CAFs, making the certificate model more robust, and updating code style for clarity and consistency.

This improvement is mostly made because CAFs have expiration dates and fixed folio numbers. If the expiration date is reached but the folios were not fully consumed, the system will try to generate a document with following number in the sequence but an error will be raised because that number belongs to an expired CAF, althought the user had already uploaded a new CAF.
To fix this, whenever the system looks for the highest number to set to a document, it previously check if that number is between the folio numbers of a valid CAF file.

### Chilean electronic document sequence management

* Added `_get_last_sequence` method to `account_move.py` to ensure that the folio number used for Chilean electronic documents (DTE) is valid and corresponds to an available CAF. If no CAF is available for the current folio, the sequence is reset using the document type's prefix and starting number.

### Certificate model validation

* Made `subject_serial_number` a required field in the `Certificate` model, enforcing that every certificate has a valid owner document and improving data integrity. We made this change to prevent the field being empty after loading the certificate in Odoo, since it is required by the SII to validate invoices.

This improvement enhances user control over cookie preferences by making
the Cookie Policy page (/cookie-policy) more accessible and allowing
users to modify their consent at any time.

**Issue:**

- Previously, the only way to access the Cookie Policy page was through
  the link in the cookie consent popup. However, once users accepted
  cookies, the popup was no longer displayed, making it impossible to
  navigate to the policy page later.

- Additionally, the Cookie Policy page had a button to reopen the cookie
  consent popup, but it was only visible if cookies were not accepted.
  Once cookies were accepted, the button was hidden, preventing users
  from changing their preferences.

**Improvements:**

- Added a permanent link to the Cookie Policy page in the copyright
  footer, ensuring it remains accessible at all times.

- The cookie consent toggle button now remains visible even after a user
  has accepted cookies, allowing them to update their preferences at any
  time.

task-[4502416](https://www.odoo.com/odoo/project/974/tasks/4502416)

Forward-Port-Of: odoo/odoo#203409