Decorator

Changed the build procedure to use pyproject.toml and moved the tests
outside of the generated wheel/tarball.

Added official support for Python 3.11, 3.12, 3.13 (thanks to Hugo van
Kemenade).

Dropped official support for Python < 3.8: the module is
expected to work on older Python versions, but I cannot test such
versions on GitHub actions, so I cannot claim that it is officially
supported.

Dafu Wu provided support for decorating partial functions, i.e.
functions wrapped by functools.partial.

Sangwoo Shim contributed a fix so that cythonized functions can be decorated.
Brian McFee pointed out an issue in the `decorator_apply` example and
Wim Glenn pointed out that the "fix" in version 5.1 broke
`decorator.contextmanager` even more. Both issues are now solved.

Added a function `decoratorx` using the `FunctionMaker` and thus
preserving the signature of `__code__` objects. Then fixed three small bugs:
- Sphinx was printing a few warnings when building the documentation, as
signaled by Tomasz Kłoczko
- functions decorated with `decorator.contextmanager` were one-shot,
as discovered by Alex Pizarro.
- `decorator.decorator` was not passing the kwsyntax argument.

Fixed a test breaking PyPy. Restored support for Sphinx.

Made the decorator module more robust when decorating builtin functions
lacking dunder attributes, like `dict.__setitem__`.

The decorator module was not passing correctly the defaults inside the
`*args` tuple, thanks to Dan Shult for the fix. Also fixed some misspellings
in the documentation and integrated codespell in the CI, thanks to
Christian Clauss.