Upgrade ruff==0.15.13

[cclauss]

Summary

Upgrade the code linter and formatter ruff in pyproject.toml:

-  "ruff==0.12.11",
+  "ruff==0.15.13",

% uv sync && uv lock
% ruff check --output-format=concise

scripts/unasync.py:59:38: B905 `zip()` without an explicit `strict=` parameter
scripts/unasync.py:70:18: B007 Loop control variable `dirnames` not used within loop body
tests/httpx2/models/test_whatwg.py:5:1: I001 [*] Import block is un-sorted or un-formatted
tests/httpx2/test_main.py:1:1: I001 [*] Import block is un-sorted or un-formatted
tests/httpx2/test_utils.py:1:1: I001 [*] Import block is un-sorted or un-formatted
tests/test_benchmark.py:1:1: I001 [*] Import block is un-sorted or un-formatted

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.

[codspeed-hq]

Merging this PR will not alter performance

✅ 7 untouched benchmarks

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_{Comparing cclauss:upgrade-ruff-0.15.13 (27c53d8) with main (d0e0f37)}