[Fix] re_cache: stop timer during async operations to prevent re-entry

[Fix] re_cache: stop timer during async operations to prevent re-entry

Stop the timer before calling exists_async and save_async to prevent
the timer from firing multiple times while an async callback is pending.
Without this, the repeating timer (0.1s interval) could fire again before
the async operation completes, causing multiple concurrent async calls
for the same re_class. This led to race conditions and use-after-free
crashes when callbacks completed out of order.