rework of random pool should be completed

[erthink]

The "random pool" used for fast creation of key-value pairs while benchmarking. In other words it is pre-generated key-value pairs, which have some predefined characteristics.

It must be:

• pseudorandom for reproducibility of benchmarks;
• not contain duplicate keys (taking into account the specified length) for workability of testcases;
• cheap by cpu and memory (include bandwidth) for correctness of results;
• distributed uniformly;
• organized into non-overlapping clusters for parallel multithreading testcases;

Current implementation:

• does not guarantee uniqueness, especially for short keys;
• uses a lot of memory, e.g. N * (key_size + value_size);

I have some idea how to do this. But it will require abandoning terminating zero at end of the keys and values.