Fix warnings from clippy 1.77

[Philippe-Cholet]

I triggered CI to see it fail: https://github.com/rust-itertools/itertools/actions/runs/8389675477/job/22976363676
Then I fixed the warnings (denied by CI).

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 94.35%. Comparing base (6814180) to head (9d297fe).
Report is 41 commits behind head on master.

Additional details and impacted files

@@ Coverage Diff @@ ## master #908 +/- ## ========================================== - Coverage 94.38% 94.35% -0.03%  ========================================== Files 48 48 Lines 6665 6807 +142 ========================================== + Hits 6291 6423 +132  - Misses 374 384 +10 

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[phimuemue]

Thanks.