Drop Python 3.10 support after its end-of-life

[m96-chan]

Tracking issue. Do not act on this before Python 3.10 actually reaches end-of-life.

Timing

Per the CPython version status page, as of 2026-09-05:

Version	Status	End of life
3.9	end-of-life	2025-10-31
3.10	security	2026-10 (scheduled)
3.11	security	2027-10
3.12	security	2028-10
3.13	bugfix	2029-10
3.14	bugfix	2030-10

3.10 is still in its security phase and is not EOL yet. The devguide shows the date in italics, meaning it is scheduled and can move, so confirm the actual date before starting rather than assuming a specific day in October.

What to change when the time comes

Drop 3.10:

• pyproject.toml — requires-python = ">=3.10" → ">=3.11"
• pyproject.toml — remove the Programming Language :: Python :: 3.10 classifier
• .github/workflows/ci.yml — two matrices (build-wheels, test-python), both at python-version: ["3.10", ...]
• .github/workflows/release.yml — one matrix
• .github/workflows/test-release.yml — one matrix

This is a breaking change for anyone still on 3.10, so it wants a version bump beyond a patch release (currently 3.0.2).

Also fix at the same time: linter targets are stale today

Independent of the 3.10 decision, both linters are configured against a Python version that is already end-of-life:

requires-python = ">=3.10"

[tool.black]
target-version = ["py39", "py310", "py311", "py312"]   # py39 is EOL; py313/py314 missing

[tool.ruff]
target-version = "py39"                                 # py39 is EOL (2025-10-31)

So the project is linted for 3.9 while requiring 3.10+, and black is not told about the 3.13/3.14 the project ships wheels for. These should be aligned with whatever requires-python ends up being.

Note that raising the ruff target enables additional pyupgrade rules, which will surface new lint errors that need fixing in the same change. That is why this was deliberately left out of the CI-unblocking work in #71 and #73 — it is a behavioural change to linting, not a fix.

[m96-chan]

The linter half of this is done in #75, merged.

All three tools were pointed at Python 3.9 (EOL 2025-10-31), not just the two named here — mypy had python_version = "3.9" as well. black and ruff now infer the target from project.requires-python instead of duplicating it, so they cannot drift again; mypy does not support inference and is pinned to 3.10 with a comment. Raising the targets produced no new findings: ruff passes (the codebase already uses X | Y everywhere, zero Optional[]/Union[]), black leaves all 54 files unchanged, and mypy reports the same 73 pre-existing errors.

Retitled, because what is left is only the 3.10 drop, and that is still blocked: 3.10 is in its security phase until 2026-10.

When it does go EOL, the linter side needs nothing beyond bumping requires-python to ">=3.11" — black and ruff follow it automatically now. Only [tool.mypy] python_version still has to be edited by hand alongside it.