Add auto-updates for PHARs

[eduardocruz]

PHPX should periodically check if newer versions of PHARs are available.

Requirements

• Store the last check timestamp for each PHAR
• Check for updates periodically (e.g., once a day)
• Add a --update-phars flag to force an update check
• Show a notification when updates are available
• Add a --no-update-check flag to skip update checking

Implementation approach

We could implement a system similar to Composer's approach:

1. Store metadata about each PHAR, including last update check
2. Check GitHub releases API or download headers to see if newer versions exist
3. Provide clear notifications when newer versions are available
4. Allow users to control update behavior with flags

This would ensure users always have access to the latest tools without manual intervention.