Rewrite closure cells in decorated methods

[Sean-Kenneth-Doherty]

Summary

• Recursively inspect wrapped/nested functions when rewriting stale __class__ closure cells for slotted classes.
• Preserve the existing classmethod, staticmethod, property, cached-property, and method handling while also following closures and __wrapped__ links.
• Add a regression for a decorated method using zero-argument super().

Fixes #1038.

Tests

• PYTHONPATH=src python - <<'PY' ... manual issue reproducer now prints A instead of raising TypeError
• uv run --group tests pytest tests/test_slots.py::TestClosureCellRewriting -q
• uv run --group tests pytest tests/test_slots.py -q
• uv run --group tests pytest -q
• uv run --group dev ruff check src/attr/_make.py tests/test_slots.py
• uv run --group dev ruff format --check src/attr/_make.py tests/test_slots.py
• python -m compileall -q src/attr/_make.py tests/test_slots.py
• git diff --check

[Sean-Kenneth-Doherty]

Pushed e26ac66 to cover the missing coverage branch in _closure_cells.

The failed coverage job reported only src/attr/_make.py:565 as missing. The added regression creates a self-referential __wrapped__ chain and verifies _closure_cells() stops revisiting wrapped functions.

Local validation after the push:

• uv run --group tests pytest tests/test_slots.py::TestClosureCellRewriting -q -> 9 passed
• uv run --group tests pytest tests/test_slots.py -q -> 58 passed, 1 skipped
• uv run --group tests pytest -q -> 1390 passed, 5 skipped, 1 xfailed
• uv run --group dev ruff check src/attr/_make.py tests/test_slots.py -> passed
• uv run --group dev ruff format --check src/attr/_make.py tests/test_slots.py -> passed
• python -m compileall -q src/attr/_make.py tests/test_slots.py -> passed
• git diff --check -> passed
• Targeted coverage run no longer lists line 565 as missing.