- variants: use direct tuple comparison instead of format! string, add sort() after dedup
- Memory section: sort rows by (test_name, backend, variant) before output
- Extra Metrics section: sort rows by (test_name, variant_label) before output
- add [lib] target to Cargo.toml to enable unit tests
- add regression test: same data in different input order produces identical report
Replace `static mut OLD_SIGBUS_HANDLER` with AtomicU8 + AtomicPtr to
remove data race UB when concurrent benchmarks call open() from multiple
threads.
Key changes:
- Use `Once::call_once` to guarantee single handler installation
- Publish old handler to atomics BEFORE installing new handler (closes
the handler-active-but-state-unpublished race window)
- Read atomics with Acquire in signal handler (async-signal-safe)
- Align si_addr to page boundary before mmap(MAP_FIXED)
- Add concurrent test: 8 threads open all 5 variants simultaneously
