pref(rocksdb): enable async io for iterators

[shumkov]

Issue being fixed or feature implemented

Writes are not blocking in RocksDB but reads are blocking. There is an asynchronous IO provided for multi-gets and iterators. That should speed up query operations in Drive which are utilizing iterators. It should increase CPU consumption though.

More details:

• https://rocksdb.org/blog/2022/10/07/asynchronous-io-in-rocksdb.html
• https://docs.rs/rocksdb/latest/rocksdb/struct.ReadOptions.html#method.set_async_io

What was done?

• Enabled async io for RocksDB iterators
• Benchmarks to prove that this option speeds up Drive's queries.

How Has This Been Tested?

With tests.

Breaking Changes

None

Checklist:

• I have performed a self-review of my own code
• I have commented my code, particularly in hard-to-understand areas
• I have added or updated relevant unit/integration/functional/e2e tests
• I have made corresponding changes to the documentation

For repository code-owners and collaborators only

• I have assigned this pull request to a milestone

[fominok]

As far as I understand RocksDB loads more data than possibly needed to reduce the number of disk reads, and those pre-fetches are blocking. If this change allows it to load subsequent data while we're processing current data then I see no harm in it, though PR title is a bit misleading since we introduce no "async io" to GroveDB, just some background processing out of our control.

@QuantumExplorer what do you think?