Feature: `sconcat` and `stimes`.

[kindaro]

Resolve #288.

There are two commits here.

• Commit № 1 adds two new benchmarks in the Pure section: one for sconcat and one for stimes.
• Commit № 2 adds specialized implementation of sconcat and stimes to the instance of Semigroup for strict Text.

The benchmarks can be run like so:

first_commit_hash='180645e'
pattern='$2 == "Pure" && ($4 == "sconcat" || $4 == "stimes") && $5 != "LazyText"'
git checkout "$first_commit_hash" &&
    cabal run text-benchmarks -- --pattern "$pattern" --timeout 10s --csv benchmarks.csv
git switch feature-sconcat-stimes &&
    cabal run text-benchmarks -- --pattern "$pattern" --timeout 10s --baseline benchmarks.csv --fail-if-slower 110

This will take a few minutes. You should see better times almost everywhere — only the tiny.sconcat will show worse times.

This is the report as seen on my machine:

All
  Pure
    tiny
      sconcat
        Text: FAIL
          38.6 ns ± 2.3 ns, 148% more than baseline
          Use -p '(($2=="Pure"&&($4=="sconcat"||$4=="stimes"))&&$5!="LazyText")&&/tiny.sconcat.Text/' to rerun this test only.
      stimes
        Text: OK
          70.7 ns ± 2.9 ns, 83% less than baseline
    ascii-small
      sconcat
        Text: OK
          18.6 μs ± 148 ns, 99% less than baseline
      stimes
        Text: OK
          125  μs ±  10 μs, 59% less than baseline
    ascii
      sconcat
        Text: OK
          28.7 ms ± 2.4 ms
      stimes
        Text: OK
          63.3 ms ± 5.6 ms, 78% less than baseline
    english
      sconcat
        Text: OK
          1.07 ms ± 7.4 μs
      stimes
        Text: OK
          4.40 ms ± 373 μs, 69% less than baseline
    russian
      sconcat
        Text: OK
          2.45 μs ± 224 ns, 95% less than baseline
      stimes
        Text: OK
          15.9 μs ± 736 ns, 62% less than baseline
    japanese
      sconcat
        Text: OK
          4.17 μs ± 175 ns, 97% less than baseline
      stimes
        Text: OK
          15.7 μs ± 1.4 μs, 63% less than baseline