build!: drop python 3.9 and 3.10, drop pyside2, require >=3.11

[tlambert03]

Drops Python 3.9/3.10 and moves the floor to >=3.11, plus the ruff updates that fall out of it.

⚠️ This also drops PySide2

Not a choice so much as a consequence: PySide2 5.15.2.1 declares requires_python: ... <3.11 and ships no wheel past cp310. It cannot be installed on the new floor, so its extra, dependency-group and CI jobs are all dead weight. Removing it also lets us delete the test-qt-legacy group and the [tool.uv] conflicts block from #743, which existed only to hold PySide2 on pytest-qt 4.4.

Changes

Version floor

• requires-python = ">=3.11", 3.9/3.10 classifiers removed
• CI: base matrix 3.10→3.11, min-deps 3.9→3.11, pyqt5 job 3.9→3.11, test-dependents default 3.10→3.11 (it would otherwise try to install magicgui on 3.10)
• SLOTS is unconditional now; the <3.11 weakref_slot skip is dead code
• PyQt5 is untouched — it supports 3.11+, only its job's Python moved

Ruff

• target-version py39→py311
• Dev toolchain re-pinned to what pre-commit already runs. These had drifted badly: ruff>=0.8.3 resolved to 0.15.12 locally while pre-commit pinned 0.16.4 — different enough that RUF036 is preview in one and stable in the other, so uv run ruff and CI disagreed about the codebase.
• 91 autofixes: Callable → collections.abc, typing_extensions → typing where 3.11 suffices, zip(..., strict=False) (explicit, behavior-preserving), one dead type: ignore

Two rules deliberately disabled

UP007/UP045 (Optional[X] → X | None) are in ignore, because for this codebase they are not a cosmetic change:

get_origin(Union[int, None]) is Union   # True
get_origin(int | None) is Union         # False on 3.11-3.13, True on 3.14

magicgui compares get_origin(...) is Union in four places, so PEP 604 unions take a different path. Letting ruff apply these broke 7 tests in test_ui_field.py — it rewrote Optional[int] to int | None and UiField then extracted a different annotation. Tests also deliberately exercise both spellings, so blanket-rewriting them would quietly cost coverage.

TC003 — collections.abc is added to flake8-type-checking.exempt-modules, alongside the typing/typing_extensions that ruff exempts by default. These 16 findings only appeared because Callable moved off typing; magicgui resolves annotations at runtime, so those names must stay importable at runtime rather than move into TYPE_CHECKING.

Known pre-existing bug (not fixed here)

The above uncovered a real bug on main, unrelated to this PR:

@magicgui
def f(x: Optional[int] = None): ...   # .annotation -> int          ✅

@magicgui
def f(x: int | None = None): ...      # .annotation -> int | None   ❌

PEP 604 unions aren't unwrapped by the four get_origin(...) is Union checks on Python 3.11–3.13 (masked on 3.14, where types.UnionType became typing.Union). Worth its own PR; happy to write it.

Testing

Full suite green on 3.11 / 3.13 / 3.14, across PyQt6, PyQt5, PySide6. prek run -a clean.

🤖 Generated with Claude Code

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 89.31%. Comparing base (128e4ba) to head (2ca01a9).

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #745      +/-   ##
==========================================
- Coverage   89.32%   89.31%   -0.02%     
==========================================
  Files          40       40              
  Lines        4835     4849      +14     
==========================================
+ Hits         4319     4331      +12     
- Misses        516      518       +2     

☔ View full report in Codecov by Harness.
📢 Have feedback on the report? Share it here.

🚀 New features to boost your workflow:

• ❄️ Test Analytics: Detect flaky tests, report on failures, and find test suite problems.

[larsoner]

I dropped PySide2 in PyVistaQt as well, no regrets! 😄