feat: Update checkpoints and improve error messages

- Updates `include/checkpoints.php` with a comprehensive list of checkpoints up to height 1,240,000.
- Adds a formatted timestamp comment to every checkpoint entry for clarity.
- Aligns all comments in `checkpoints.php` for improved readability.
- Improves the error message for the genesis block check in `include/init.inc.php` to provide more specific details.
- Enhances the log message in `include/class/NodeSync.php` to give a more detailed output for checkpoint validation.

Author: google-labs-jules[bot]