clippy: fix warnings from assert_is_empty lint

[cakebaker]

This PR fixes three warnings from the assert_is_empty lint that show up with Rust 1.99.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 83.86%. Comparing base (95804a2) to head (27bd13d).

Additional details and impacted files

@@           Coverage Diff           @@
##             main     #588   +/-   ##
=======================================
  Coverage   83.86%   83.86%           
=======================================
  Files          14       14           
  Lines        7203     7203           
  Branches      424      424           
=======================================
  Hits         6041     6041           
  Misses       1157     1157           
  Partials        5        5           

Flag	Coverage Δ
macos_latest	84.98% <ø> (ø)
ubuntu_latest	85.17% <ø> (ø)
windows_latest	0.00% <ø> (ø)

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[codspeed]

Merging this PR will improve performance by 3.34%

⚠️ Different runtime environments detected

Some benchmarks with significant performance changes were compared across different runtime environments,
which may affect the accuracy of the results.

Open the report in CodSpeed to investigate

⚡ 3 improved benchmarks
✅ 8 untouched benchmarks

Performance Changes

	Benchmark	BASE	HEAD	Efficiency
⚡	access_log_no_subst	1.1 s	1.1 s	+3.45%
⚡	access_log_all_del	1.2 s	1.1 s	+3.34%
⚡	access_log_no_del	1.1 s	1.1 s	+3.24%

Tip

Curious why performance improved? Comment @codspeedbot explain why performance improved on this PR, or directly use the CodSpeed MCP with your agent.

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_{Comparing cakebaker:clippy_assert_is_empty (27bd13d) with main (95804a2)}