docs: def hash64(key, seed):
      """
      Wrapper around mmh3.hash64 to get us single 64-bit value.
  
      This also does the extra work of ensuring that we always treat the
      returned values as big-endian unsigned long, like smhasher used to
      do.
      """
      hash_val = mmh3.hash64(key, seed)[0]
      return struct.unpack('>Q', struct.pack('q', hash_val))[0]