MDEV-37605 Converting InnoDB-Based Binary Logs to Legacy Format

With MDEV-34705, MariaDB introduced the ability to store binary logs inside InnoDB tablespace files ( .ibb ) instead of traditional flat sequential files. While this brings significant performance improvements, it also creates a compatibility challenge: legacy servers and tools cannot read the new format. This project will extend mariadb-binlog to read InnoDB-format binlogs and generate legacy-format binary log files as output, ensuring backward compatibility for downgrades, migrations, and third-party tooling. Deliverables - Command line option to generate Legacy Binlog file from InnoDB based Binlog - Checksum support - Unit and Integration tests - Design documentation covering architecture, usage, and known limitations