Problem:
When applying commit timestamps to truncate entry, then entire truncate list is locked with write lock. Such a broad and powerful lock is an overkill.

Solution:
Remove the queue-wide write lock:

• Replace it with a per-entry committed state.
• Writer: on commit set start_ts and durable_ts, then set state to committed with release semantics.
• Reader: load the state with acquire semantics; if it is committed, read timestamps. Otherwise, use default WT_TS_NONE.

That gives us per-entry consistency without locking the entire queue.