Summary
- drop the `systemd` extra from `pyproject.toml` and the
`systemd-python` optional dependency
- this means we don't ship the journald log handler, so it clarifies the
docs how to install that in the venv
- ensure the Debian virtualenv build keeps shipping
`systemd-python>=231` in the venv, so the packaged log config can keep
using `systemd.journal.JournalHandler`
Context of this is the following:
> Today in my 'how hard would it be to move to uv' journey:
https://github.com/systemd/python-systemd/issues/167
>
> The gist of it is that uv really wants to create a universal lock
file, which means it needs to be able to resolve the package metadata,
even for packages locked for other platforms. In the case of
systemd-python, they use mesonpy as build backend, which doesn't
implement prepare_metadata_for_build_wheel, which means it needs to run
meson to be able to resolve the package metadata. And it will hard-fail
if libsystemd dev headers aren't available 😭
>
> [*message in
#synapse-dev:matrix.org*](https://matrix.to/#/!i5D5LLct_DYG-4hQprLzrxdbZ580U9UB6AEgFnk6rZQ/$OKLB3TJVXAwq43sAZFJ-_PvMMzl4P_lWmSAtlmsoMuM?via=element.io&via=matrix.org&via=beeper.com)
