Refactor repository structure and refresh validation evidence.

Main changes:
- move ext4_rs from third_party to kernel/libs
- update integration paths and build configuration
- refresh Phase3 xfstests evidence
- refresh Phase4 crash-recovery evidence
- update lmbench benchmark records

Validation:
- verify ext4_rs functionality after relocation
- rerun selected validation suites
- confirm benchmark reproducibility

Contest stage:
- Phase 5 repository refactoring and evidence refresh

Next steps:
- continue JBD2 journaling development
- improve xfstests pass rate
- expand performance evaluation