feat: add Python 3.15, drop Python 3.10

[henryiii]

🤖 AI text below 🤖

Adds Python 3.15 (pre-release) to the sp-repo-review classifiers and test matrix. The template and guide do not add 3.15 yet.

Drops Python 3.10:

• sp-repo-review: requires-python >=3.11. Removes the tomli dependency and the _compat package; code now imports tomllib and importlib.resources.abc directly.
• Template and guide: minimum is now 3.11 in pyproject.toml, CI matrices, the maturin abi3 feature, and the tool config examples. The GitLab CI images move from -buster (no 3.12+ images) to -bookworm, and CIBW_BUILD is now cp311–cp314.
• codespell hook: removes the tomli extra dependency.

Also fixes the nox session names in AGENTS.md.

Ran tests, lint and dist sessions for hatch and maturin, and compare_copier, locally.

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📚 Documentation preview 📚: https://scientific-python-cookie--863.org.readthedocs.build/