seq: Add a print_seq fast path function for integer and positive increments

[drinkcat]

A lot of custom logic, we basically do arithmetic on character arrays, but this comes at with huge performance gains.

Unlike coreutils seq, we do this for all positive increments (because why not), and we don't fall back to slow path if the last parameter is in scientific notation.

Fixes #7482

---

I'm not too sure what I think about this ,-) This is a lot of added code, but this comes with huge performance gains, around 17x in some cases (and also, it was a fun puzzle, and I learnt quite a few new Rust things ,-P), and we are now competitive with GNU seq:

$ cargo build -r -p uu_seq && taskset -c 0 hyperfine --warmup 3 -L seq target/release/seq,./seq-main,seq "{seq} 1000000"
Benchmark 1: target/release/seq 1000000
  Time (mean ± σ):      10.6 ms ±   1.1 ms    [User: 9.9 ms, System: 0.7 ms]
  Range (min … max):    10.0 ms …  22.4 ms    249 runs
 
  Warning: Statistical outliers were detected. Consider re-running this benchmark on a quiet system without any interferences from other programs. It might help to use the '--warmup' or '--prepare' options.
 
Benchmark 2: ./seq-main 1000000
  Time (mean ± σ):     165.7 ms ±   5.4 ms    [User: 163.5 ms, System: 0.8 ms]
  Range (min … max):   160.8 ms … 182.3 ms    18 runs
 
Benchmark 3: seq 1000000
  Time (mean ± σ):       9.3 ms ±   0.1 ms    [User: 9.0 ms, System: 0.5 ms]
  Range (min … max):     8.8 ms …   9.5 ms    275 runs
 
Summary
  seq 1000000 ran
    1.14 ± 0.12 times faster than target/release/seq 1000000
   17.83 ± 0.60 times faster than ./seq-main 1000000

We're less conservative than GNU, so this path also activates for ranges likes 1 123 100000000 (the GNU manual says they do something special below 200 increment, but I suspect that value is lower) and 1e11, as long as the desired precision is still zero (a.k.a. integers).

Still a draft, probably want to add something to BENCHMARKING.md, a few more tests, and see if I can extract a bit more performance...

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/timeout/timeout (passes in this run but fails in the 'main' branch)