ci: pin black 26.3.1 across pre-commit and CI, drop Python 3.13

[jeremyeder]

Summary

• Upgrade black from 25.11.0 to 26.3.1 in .pre-commit-config.yaml
• Pin black==26.3.1 in CI so it matches pre-commit exactly
• Drop Python 3.13 from CI matrix — standardize on 3.12 only

The root cause: pre-commit pinned black 25.11.0, but CI ran pip install -e ".[dev]" which pulled latest black (26.3.1). The two versions disagree on multiline string list formatting, causing spurious CI failures (e.g. #416).

Test plan

• black --check . passes with 26.3.1 (154 files unchanged)
• CI passes on this PR (single 3.12 job, pinned black)

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ℹ️ Recent review info

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Configuration used: Organization UI

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📥 Commits

Reviewing files that changed from the base of the PR and between 9ada97c and 65a7702.

📒 Files selected for processing (2)

• .github/workflows/ci.yml
• .pre-commit-config.yaml

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Walkthrough

CI and pre-commit configurations are updated to standardize on Python 3.12 (replacing a 3.12/3.13 matrix) and black formatter version 26.3.1. The blocking CI job now explicitly installs black 26.3.1 after dev dependencies.

Changes

Python and Black Version Standardization

Layer / File(s)	Summary
CI job Python version consolidation .github/workflows/ci.yml	All jobs (blocking checks, comprehensive tests, macOS tests, and coverage reporting) move from 3.13 matrix entries to fixed python-version: '3.12'. Blocking job adds explicit pip install -e ".[dev]" followed by pinned black==26.3.1 installation.
Pre-commit black hook version update .pre-commit-config.yaml	Black pre-commit hook bumps from 25.11.0 to 26.3.1, aligning with the pinned version used in CI.

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🎯 1 (Trivial) | ⏱️ ~3 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Title check	✅ Passed	The title clearly and specifically describes the main changes: upgrading black to 26.3.1, pinning it across pre-commit and CI, and dropping Python 3.13 support.
Description check	✅ Passed	The description provides clear context on what changed, why it was necessary (fixing formatting disagreements between versions), and includes a test plan with verification steps.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.
Linked Issues check	✅ Passed	Check skipped because no linked issues were found for this pull request.
Out of Scope Changes check	✅ Passed	Check skipped because no linked issues were found for this pull request.

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[github-actions]

📈 Test Coverage Report

Branch	Coverage
This PR	72.5%
Main	72.5%
Diff	✅ +0%

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Coverage calculated from unit tests only

[github-actions]

🎉 This PR is included in version 2.35.3 🎉

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