chore: apply Clippy suggestions and improve code formatting

[nyurik]

No description provided.

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/tail/follow-name (fails in this run but passes in the 'main' branch)
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)

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/tail/inotify-dir-recreate (passes in this run but fails in the 'main' branch)

[codspeed-hq]

Merging this PR will not alter performance

✅ 284 untouched benchmarks
⏩ 38 skipped benchmarks¹

---

_{Comparing nyurik:clippy (76f5219) with main (d66dfe9)}

Footnotes

1. 38 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. ↩

[github-actions]

GNU testsuite comparison:

Skipping an intermittent issue tests/tail/follow-name (passes in this run but fails in the 'main' branch)

[xtqqczze]

@nyurik I've been fixing some clippy lints, I usually stick to 1 lint per PR for ease of review

[nyurik]

@xtqqczze thx, makes sense. I moved a big number formatting change into #10717 making this PR only 50 line changes - hopefully makes it much easier to review

[github-actions]

GNU testsuite comparison:

Skip an intermittent issue tests/shuf/shuf-reservoir (fails in this run but passes in the 'main' branch)
Skip an intermittent issue tests/sort/sort-stale-thread-mem (fails in this run but passes in the 'main' branch)

[sylvestre]

please document "why"

[nyurik]

I'll add a comment - but the extended version: this is what it would look like after optimization -- i don't think it's as readable

        [b'l' | b'r' | b'e', b'c']
            | [b'r', b's']
            | [b'n' | b's' | b'd', b'o']
            | [b'f' | b'd' | b'p' | b'm', b'i']
            | [b'l', b'n']
            | [b'b' | b'c', b'd']
            | [b'o', b'r' | b'w']
            | [b'e', b'x']
            | [b's', b'u' | b'g' | b't']
            | [b't', b'w']
            | [b'c', b'a' | b'l']
            | [b'm', b'h']

[sylvestre]

seems unrelated?