Use UnsignedBytes comparator from Guava

[phearnot]

UnsignedBytes.lexicographicalComparator from Guava offers better performance when comparing random byte strings, as well as in a worst case when byte strings differ only in the last bytes.

[info] Benchmark                                                       Mode  Cnt    Score   Error   Units
[info] ByteArrayComparePerformance.compareWithUnsignedBytesRandom     thrpt   20  102.230 ± 0.733  ops/ms
[info] ByteArrayComparePerformance.compareWithUnsignedBytesWorstCase  thrpt   20   79.906 ± 0.980  ops/ms
[info] ByteArrayComparePerformance.legacyCompareRandom                thrpt   20   82.349 ± 0.486  ops/ms
[info] ByteArrayComparePerformance.legacyCompareWorstCase             thrpt   20   20.998 ± 0.163  ops/ms