This makes it easier for people to interact with the project in
a unified manner.

Unfortunately tox does not play very nicely with Poetry. Tox was mostly
useful since it managed virtual environments, however now this is done
by Poetry.

Thus we do not anymore need it since we can run our commands using
`poetry run`. I have extended the internal helper tool 'project' with
those commands that have previously been run using tox.

Changed the logic so that it isn't testing repeatedly for the correct matrix version, and since we're using poetry instead of pipx, changed the action

This reverts commit 913f856.

This reverts commit c3b6f07.

This commit hardcoded the paths that `isort` and `black` checks. This
means that the `check-format` job will act on the entire codebase
instead of only changed files. We need to define a `path` argument with
a default value in order to achieve the above.

Regarding "." vs "beets beetsplug test", the intention behind using "."
was to also check python files like `docs/conf.py` and
`extra/release.py` which I presume we would also want to format
properly.

This reverts commit fc373f5.

See CONTRIBUTING.rst which has tools setup guidelines for users. They
are expected to install both poetry and poethepoet globally in their
system.

This reverts commit af996f4.

Since `poethepoet` is installed globally in the workflows, running it
does not require `poetry run` suffix. This is actually one of the
reasons why it's preferable to have this tool installed globally.

This reverts commit 4550d39.

I love this attempt to DRY-up the linting workflow! I remember back in
the day also initially assuming that this is how the jobs work. However,
I had to meet the harsh reality of each job needing to be set up from
zero. :(

This reverts commit 5526bd3.

Poetry must be installed before `setup-python` action, weirdly. And we
need to install poethepoet globally too!