Reduce statistics visits and visitors identifiability

[giuscris]

This pull request updates the visitor tracking logic in the Statistics module to improve uniqueness and future-proof the identification of visitors. The main changes focus on replacing the legacy IP-based visitor keys with a new approach that incorporates the date and user agent, and introduces a migration step to handle existing data. In this way, visitors become less identifiable over time, as the anonymized IP address and user agent are hashed together with the current date, producing rotating, non-persistent identifiers instead of stable tracking keys.

Visitor tracking improvements:

• Visitor hash generation now includes the date, anonymized IP, URI, and user agent, making visitor identification more robust and less reliant solely on IP address. (formwork/src/Statistics/Statistics.php, formwork/src/Statistics/Statistics.phpR64-R72)
• Visitor registry keys are now based on a hash of the date, IP, and user agent, rather than just the IP, which helps reduce false positives for unique visits. (formwork/src/Statistics/Statistics.php, formwork/src/Statistics/Statistics.phpL82-R104)

Legacy data migration:

• Added logic to migrate legacy visitor keys based on IP to the new hash-based format, ensuring backward compatibility and a smooth transition. This migration code is marked for removal in a future major release. (formwork/src/Statistics/Statistics.php, formwork/src/Statistics/Statistics.phpL82-R104)

[Copilot]

Pull request overview

This PR updates Formwork’s Statistics visitor tracking to reduce long-lived visitor identifiability by rotating identifiers (daily) and incorporating the user agent, while migrating existing visitor registry entries keyed by anonymized IP.

Changes:

• Include $date and $userAgent in the per-page session hash used for visit de-duplication.
• Replace legacy IP-based visitor registry keys with a daily rotating hash of date + anonymized IP + user agent.
• Add an in-place migration step to convert existing visitors entries from $ip keys to the new hashed keys.

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