[avgvi]

The type stubs reject default=None in incr and decr, which the code has always accepted: with default=None a missing or expired key raises KeyError instead of starting from a default. BaseCache in _types.pyi typed default as int, so mypy reports an arg-type error on a call such as cache.incr(key, 1, default=None):

Argument "default" to "incr" of "BaseCache" has incompatible type "None"; expected "int"  [arg-type]

This showed up when moving ai-marketplace-monitor to 5.8.2: its two counter calls in utils.py pass default=None, and the only way through was # type: ignore[arg-type].

• Stub: BaseCache.incr and decr take default: int | None. Cache and FanoutCache inherit both and don't redeclare them. DjangoCache already accepted None, and the recipes don't declare either method.
• Check: a new tests/typecheck_stubs.py holds calls that must type-check against the stubs: incr and decr with default=None on Cache and FanoutCache. tox -e mypy, and so the CI lint job, now checks it next to the package. pytest doesn't collect it.
• Changelog: a CHANGELOG.md entry under Unreleased.

The runtime code is unchanged.

Checked:

• tox -e mypy fails with the error above on the four new calls against the old stub, and passes here (mypy 2.4.1).
• bluecheck, flake8, isortcheck, mypy and pylint pass.
• The full test suite passes on Python 3.12 with Django 5.2 (815 passed, 2 skipped, 99% coverage).
• stubtest reports the same on master and on this branch.

Possible follow-ups, not in this PR:

• FanoutCache.incr and decr return None on a database timeout, but the stub says int.
• The incr docstrings pass a float delta, which works at runtime, but the stubs allow only int.
• __init__.pyi leaves out DjangoCache, which is exported when Django is installed, so stubtest reports it. stubtest doesn't run in CI.