Implement journaling support

[jserv]

Originally implemented in ext3, the ext4 filesystem utilizes a journal to safeguard against metadata inconsistencies following a system crash. While the earlier version of simplefs (journal-v6 branch) supported journaling through the jbd2 -- allowing for the reservation of file system blocks within the filesystem to expedite the on-disk writing of critical data -- this feature was lost when the repository was completely overhauled to support newer Linux kernel versions.

The time has come to upgrade this project by reintegrating jbd2 for enhanced journaling capabilities.