Ruby 2.4.0 introduced `String#unpack1`, which is faster than `String#unpack[0]`

[Petr Pučil]

We're probably not ready to end support for Ruby versions older than 2.4 (yet), but when we are, we could make methods for reading integers faster by switching to String#unpack1 - see https://github.com/fastruby/fast-ruby#stringunpack1-vs-stringunpack0-code:

Comparison:
      String#unpack1:  4864467.2 i/s
    String#unpack[0]:  3777815.6 i/s - 1.29x  slower

According to the above benchmark, String#unpack1 may be 29% faster.