Fix tiered memory race conditions and corruption issues

Key changes:
- Remove mprotect from CLOCK algorithm (was incorrectly protecting hot segments)
- Update SIGSEGV handler to allow promotion to proceed without aborting
- Add unprotect before promotion copy to prevent SIGSEGV during data copy
- Add segment locking to combine cleaner to prevent eviction during combine
- Add promotion check in update_cell_by for old segment access
- Disable page_fault_tracking by default to avoid signal handler overhead

This fixes the race condition where code could read garbage from cold segments
and the SIGSEGV crashes during promotion.

Author: shisoft