Rust: Use Vec<u8> instead of String

There is no need to use String here because it doesn't need to handle with UTF-8 text.

( BTW, I suggest formatting the rust code with rustfmt.

Before

    C++98_omp: top:   82.73, min:   79.20, avg:   87.43, max:  105.61, mdev:    6.41, cnt:  20
Rust_parallel: top:   95.32, min:   94.08, avg:   98.42, max:  111.41, mdev:    4.18, cnt:  20
        C++98: top:  170.72, min:  168.93, avg:  173.83, max:  182.70, mdev:    3.76, cnt:  20
  C++14_boost: top:  172.58, min:  170.67, avg:  180.63, max:  239.08, mdev:   14.53, cnt:  20
        C++17: top:  173.47, min:  171.96, avg:  176.69, max:  186.13, mdev:    3.74, cnt:  20
        C++14: top:  174.28, min:  171.19, avg:  183.63, max:  252.61, mdev:   21.38, cnt:  20
         Rust: top:  198.10, min:  196.08, avg:  201.74, max:  211.39, mdev:    4.52, cnt:  20
            C: top:  198.58, min:  196.73, avg:  203.29, max:  222.99, mdev:    6.34, cnt:  20
        C++11: top:  213.94, min:  209.16, avg:  237.94, max:  416.80, mdev:   55.03, cnt:  20

After

Rust_parallel: top:   79.45, min:   78.25, avg:   83.44, max:   94.88, mdev:    5.35, cnt:  20
    C++98_omp: top:   82.37, min:   78.13, avg:   87.86, max:  113.53, mdev:    7.93, cnt:  20
        C++98: top:  170.59, min:  169.05, avg:  175.21, max:  184.32, mdev:    5.04, cnt:  20
  C++14_boost: top:  171.42, min:  170.71, avg:  176.53, max:  190.11, mdev:    6.00, cnt:  20
         Rust: top:  172.00, min:  171.09, avg:  176.22, max:  188.22, mdev:    5.35, cnt:  20
        C++14: top:  172.30, min:  171.25, avg:  176.92, max:  189.03, mdev:    5.71, cnt:  20
        C++17: top:  173.76, min:  172.32, avg:  178.25, max:  191.65, mdev:    5.40, cnt:  20
            C: top:  199.71, min:  197.93, avg:  204.85, max:  219.96, mdev:    6.42, cnt:  20
        C++11: top:  210.57, min:  208.94, avg:  215.75, max:  234.08, mdev:    6.41, cnt:  20

lilydjwg / swapview-rosetta

Rust: Use Vec<u8> instead of String #161