shuf: Tune performance for -i 1-1000000

[oech3]

Should split cgu=1 unrelated things from #10476 for shuf.

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/shuf/shuf-reservoir (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/sort/sort-stale-thread-mem (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/tty/tty-eof (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/tail/retry is no longer failing!

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/shuf/shuf-reservoir (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/sort/sort-stale-thread-mem (passes in this run but fails in the 'main' branch)
Skipping an intermittent issue tests/tty/tty-eof (passes in this run but fails in the 'main' branch)
Congrats! The gnu test tests/tail/retry is no longer failing!

[github-actions]

GNU testsuite comparison:

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

[codspeed-hq]

CodSpeed Performance Report

Merging this PR will improve performance by 17%

_{Comparing oech3:cold (f33df28) with main (c279ede)}

Summary

⚡ 2 improved benchmarks
✅ 140 untouched benchmarks
⏩ 180 skipped benchmarks¹

Performance Changes

	Mode	Benchmark	BASE	HEAD	Efficiency
⚡	Simulation	shuf_repeat_sampling[50000]	5.2 ms	4.7 ms	+9.05%
⚡	Simulation	shuf_lines[100000]	31.7 ms	27.1 ms	+17%

Footnotes

1. 180 benchmarks were skipped, so the baseline results were used instead. If they were deleted from the codebase, click here and archive them to remove them from the performance reports. ↩

[oech3]

@blyxxyz Would you review this (without cgu=1)? I'm not familiar with shuf...

[sylvestre]

the commit needs to explain the shuf change, not what you are trying to achieve

[oech3]

the commit needs to explain the shuf change, not what you are trying to achieve

Is shuf: performance tuning OK?

[github-actions]

GNU testsuite comparison:

Note: The gnu test tests/dd/no-allocate is now being skipped but was previously passing.

[github-actions]

GNU testsuite comparison:

Note: The gnu test tests/env/env-signal-handler is now being skipped but was previously passing.

[github-actions]

GNU testsuite comparison:

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

[blyxxyz]

Looks good!

[github-actions]

GNU testsuite comparison:

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