pub fn set_multi_get_chunk_size(&mut self, chunk_size: usize) {
        self.multi_get_chunk_size = chunk_size;
    }
Sets the chunk size for multi-get operations. The requested keys will be split
into chunks of this size and requested in parallel using `rayon`. Setting chunk size
to a large value (e.g., `usize::MAX`) will effectively disable parallelism.

[RocksDB docs] claim that multi-get operations may be parallelized internally,
but this seems to be dependent on the env; it may be the case that (single-threaded)
I/O parallelization is only achieved using `liburing`, which requires enabling
the `io-uring` feature of `rocksdb` crate and is only available on Linux.
Thus, setting this value to around `100..1_000` can still lead to substantial
performance boost (order of 2x) in some environments.

[RocksDB docs]: https://github.com/facebook/rocksdb/wiki/MultiGet-Performance
core/lib/zk_os_merkle_tree/src/storage/rocksdb.rs