Add a wyhash seed_init()

https://github.com/ManDeJan/zig-wyhash/issues/2 applies to you also.
When your random initial seed hits one of the bad seeds by chance the results are bad.
Not really security relevant, and easy to fix. But annoying. key independent collisions, so vuln. to DDOS.
Esp. the 64bit variant has a lot of bad seeds, like 2^33.