Putting NM to sleep now says "off" instead of "sleep".

Fixes

> ISC004 Unparenthesized implicit string concatenation in collection

with latest ruff.

Fixes most of "RUF067 `__init__` module should only contain docstrings
and re-exports" with current upstream ruff.

We really want `__version__`, so ignore that.

Most recent ruff complains about

> PYI034 `__enter__` methods in classes like `SpawnedMock` usually return `self` at runtime
> help: Use `Self` as return type

But neither `Self` nor `self` nor `"Self"` actually works. Let's not
bother, mypy figures out the return type just fine.

This is what systemd calls these days.

`systemctl suspend` and friends call this. Add a test case.

 - The Suspend() functionality moved from UPower to systemd-logind ages
   ago. Move the examples to that.

 - Make the examples actually work unmodified by addig a `busctl` call as a
   placeholder for what your tested program would do.

 - Move from tearDown() to addCleanup(), which is is the modern style.

 - Rewrite the pytest example to use the current API.

Fixes #236

This extracts the examples into temporary files and runs them through
pytest. Let's make sure that these don't break again in the future!

This quiesces a deprecation warning

> The configuration option "asyncio_default_fixture_loop_scope" is unset.

This project does not use asyncio, this just happens because I have
the package installed locally.

This happens in wheel installs in Debian's `pybuild` environment.