Icontract

=====
* Fixed invariants leak between related classes (297)

This is a critical bugfix patch version. We introduced a bug in

=====
* Allowed to enforce invariants on attribute setting (292)

Originally, we had enforced invariants only at calls to "normal"
methods, and excluded ``__setattr__`` since it is usually too expensive
to verify invariants whenever setting an attribute.

However, there are use cases where the users prefer to incur to
computational overhead for correctness. To that end, we introduced the
feature to steer when the invariants are enforced (at method calls,
on setting attributes, or in both situations).

=====
* Updated typeguard and deal to latest versions (284)

This change is needed so that distributions can successfully run
the necessary tests with the development dependencies. Previously,
the dependencies were outdated, and the old versions were already
deprecated in distributions (notably, typegard and deal).

=====
* Added Python 3.11 to the list of supported Pythons (280)
* Fixed deal dependency marker (279)

This patch is important as we silently broke ``setup.py``, which was
tolerated by older versions of setuptools, but not any more by
the newer ones. With this patch, icontract's ``setup.py`` is made
valid again.

=====
* Restored Python 3.6 support (274)

The support for Python 3.6 has been dropped in 257 as GitHub removed
its support in the CI pipeline. With this patch, we restored
the support of Python 3.6. Notably, we had to add
the package ``contextvars`` conditioned on Python 3.6.

=====
* Removed meta data files from setup.py (262)
* Added support for python 3.11 (260)
* Fixed in-progress set for async (256)