improve(memory): keep embedding cache writes off the main thread (#16…

improve(memory): keep embedding cache writes off the main thread (#161831)

* perf(memory): move generated cache writes to publication worker

Retain the captured published database and its writer admission while staging bounded cache rows. Recheck revision and session tombstones in the native transaction, and invalidate conflicting generations before releasing admitted work or a refused publication attempt.

* test(memory): keep bound capacity fixture cleanup synchronous

Preserve the real backend close receiver and both cleanup errors. Capture the fixture before manager startup and verify the actual database source; retain the producer synchronous close type without changing emitted runtime code.