The types of objects used in pytest's API are now exported so they may be used in type annotations.

The newly-exported types are:

- ``pytest.Mark`` for :class:`marks <pytest.Mark>`.
- ``pytest.MarkDecorator`` for :class:`mark decorators <pytest.MarkDecorator>`.
- ``pytest.MarkGenerator`` for the :class:`pytest.mark <pytest.MarkGenerator>` singleton.
- ``pytest.Metafunc`` for the :class:`metafunc <pytest.MarkGenerator>` argument to the `pytest_generate_tests <pytest.hookspec.pytest_generate_tests>` hook.
- ``pytest.runner.CallInfo`` for the :class:`CallInfo <pytest.CallInfo>` type passed to various hooks.

Constructing them directly is not supported; they are only meant for use in type annotations.
Doing so will emit a deprecation warning, and may become a hard-error in pytest 7.0.

Subclassing them is also not supported. This is not currently enforced at runtime, but is detected by type-checkers such as mypy.