Optimization ideas

[igchor]

• use pmem2_memcpy_async (Consider use pmem2_memcpy_async in async_append #163) to enable nontemporal stores. Possibly we might need to add extra threshold to perform memcpy using temporal stores.
• process timestamps in batches of arbitrary size during commit/persist operations (to increase concurrency - currently, thread tries to acquire as many timestamps as possible which might result in other threads waiting instead of doing actual work) (Commit/persist batch processing #245)
• properly use notifier in wait_committed/wait_persisted - this can be especially important for SPDK integration (?)

DSA specific:

• use batching (once implemented in miniasync or use DML directly)
• for small appends, use normal mempcy and DML persist operation in background (combine multiple persists into one in software)