introducing wyhash hash function

Dear All:
I would like to introduce wyhash (https://github.com/wangyi-fudan/wyhash)
It is a 64-bit little endian portable hash function. It is the fastest one that passed all strict hash function tests (https://github.com/rurban/smhasher). I thinkfoundationdb can make use of it to increase performance.

Start by reading the wyhash project and its linked smhasher results to understand the proposed 64-bit hash function and its performance claims. Then identify where FoundationDB could use it; the issue does not name an entry point, tests, benchmark, or a concrete definition of done.

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