Write some benchmark tests

[lvjr]

We need some benchmark tests for future performance improvement.

Yes, l3regex is quite slow. And I have to improve the speeds of codehigh and tabularray packages by using less l3regex and less loops. As a first step I need to write some benchmark tests.

Originally posted by @lvjr in https://github.com/lvjr/tabularray/discussions/370#discussioncomment-5114567

[lvjr]

The problem is that l3benchmark is not so accurate, even on Linux. Last year I ran the same benchmark test several times on Overleaf TeXLive 2022 and got the following output:

  0.0139 seconds (4.7e4 ops)
  0.425 seconds (1.58e6 ops)
  0.00421 seconds (1.15e4 ops)
  0.446 seconds (1.01e6 ops)
  0.00366 seconds (7.61e3 ops)
  0.433 seconds (8.88e5 ops)
  0.0027 seconds (9.92e3 ops)
  0.368 seconds (1.37e6 ops)
  0.00261 seconds (9.65e3 ops)
  0.423 seconds (1.57e6 ops)
  0.0027 seconds (1e4 ops)
  0.368 seconds (1.36e6 ops)

See also https://github.com/latex3/latex3/issues/1182 .