Drop Python 3.9, add Python 3.13 and 3.14 support

[amc-corey-cox]

Summary

• Bump minimum Python from ^3.9 to ^3.10 (3.9 reached EOL October 2025)
• Add Python 3.13 and 3.14 to classifiers and CI matrix
• Remove continue-on-error for 3.13 (stable since Oct 2024)
• Bump GitHub Actions to current versions: checkout v4, setup-python v5, cache v4

Closes #182
Part of release plan for v0.5.4-rc2 (#181)

Test plan

• CI passes on all matrix combinations (3.10–3.14 x ubuntu/windows)

[Copilot]

Pull request overview

Updates the project’s declared and tested Python support to drop EOL Python 3.9 and add support for newer Python versions, aligning packaging metadata, dependency locking, and CI.

Changes:

• Bump minimum supported Python from ^3.9 to ^3.10 and update Trove classifiers through 3.14.
• Regenerate poetry.lock under the new Python constraint / newer Poetry version.
• Update PR CI matrix to test Python 3.10–3.14 and bump core GitHub Actions versions.

Reviewed changes

Copilot reviewed 2 out of 3 changed files in this pull request and generated 2 comments.

File	Description
pyproject.toml	Drops 3.9, sets Python requirement to ^3.10, adds classifiers for 3.13/3.14.
poetry.lock	Lockfile regenerated (Poetry 2.3.2) consistent with ^3.10 minimum and updated deps/markers.
.github/workflows/check-pull-request.yaml	Updates CI matrix (3.10–3.14), bumps actions versions, adds runtime diagnostics, changes continue-on-error behavior.

Comments suppressed due to low confidence (1)

.github/workflows/check-pull-request.yaml:63

• The cache key for .venv does not include matrix.python-version, so a venv built under one Python version can be restored for a different version on the same OS. That can cause flaky CI and import/ABI issues for compiled deps (e.g., lxml/numpy/greenlet). Include ${{ matrix.python-version }} (and optionally architecture) in the cache key (and restore-keys if desired).

      - name: Load cached venv
        id: cached-poetry-dependencies
        uses: actions/cache@v4
        with:
          path: .venv
          key: venv-${{ runner.os }}-${{ hashFiles('**/poetry.lock') }}

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