Closes #190

Description

Use circlehash.Hash64Uint64x2() which accepts two uint64 values to hash. This avoids the need to create a new 16-byte slice and concatenation.

This code block is eliminated:

sIDBytes := make([]byte, storageIDSize)
_, err = sID.ToRawBytes(sIDBytes)
require.NoError(b, err)

Benchmark comparison on Haswell CPU with Go 1.16.9:

name             old time/op    new time/op    delta
HashSeedBytes-4     494ns ± 1%       3ns ± 0%  -99.45%  (p=0.000 n=20+19)

Hash64Uint64x2() is compatible with Hash64() for 16-byte inputs (given same inputs, they produce identical digests).

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• Code follows the standards mentioned here
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