do rchash in parallel with all available cores

[jpritikin]

Summary

It seems like rchash only uses a single core. This is a problem for old/slow CPUs that cannot complete the hash in time. If bee used all available cores then more old/slow CPUs might be able to participate in the storage game.

Motivation

Allow more nodes to participate in the storage game.

[istae]

there are currently 6 workers in the ReserveSample function so this is a parallelized process. We can do with more profiling though to see where we can improve