chore: fix clippy::single_match_else

[nyurik]

after removing single_match_else = "allow" I ran this command:

__CARGO_FIX_YOLO=1 cargo clippy --fix --all-targets --workspace

and manually fixed all the edge cases and restored some comments to the new location. No AI here :)

Overall, now the code is less nested, shorter, and cleaner to reason about. When reviewing, make sure to hide whitespace in the ⚙️ menu.

[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:clippy4 (b214fde) with main (26a29ca)}

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:

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

[sylvestre]

is it always better ? :)

[nyurik]

hard to say - I'm sure we can come up with some case when its not - but I looked through every case fixed here - seems to all make sense and all make code easier to read, less indented, and shorter overall - so I guess that lint does have some value :)