Maubot

* Updated Docker image to Alpine 3.21.
* Updated media upload/download endpoints in management frontend
(thanks to [domrim] in [253]).
* Fixed plugin web app base path not including a trailing slash
(thanks to [jkhsjdhjs] in [240]).
* Changed markdown parsing to cut off plaintext body if necessary to allow
longer formatted messages.
* Updated dependencies to fix Python 3.13 compatibility.

[domrim]: https://github.com/domrim
[jkhsjdhjs]: https://github.com/jkhsjdhjs
[253]: https://github.com/maubot/maubot/pull/253
[240]: https://github.com/maubot/maubot/pull/240

* Dropped Python 3.9 support.
* Updated Docker image to Alpine 3.20.
* Updated mautrix-python to 0.20.6 to support authenticated media.
* Removed hard dependency on SQLAlchemy.
* Fixed `main_class` to default to being loaded from the last module instead of
the first if a module name is not explicitly specified.
* This was already the [documented behavior](https://docs.mau.fi/maubot/dev/reference/plugin-metadata.html),
and loading from the first module doesn't make sense due to import order.
* Added simple scheduler utility for running background tasks periodically or
after a certain delay.
* Added testing framework for plugins (thanks to [abompard] in [225]).
* Changed `mbc build` to ignore directories declared in `modules` that are
missing an `__init__.py` file.
* Importing the modules at runtime would fail and break the plugin.
To include non-code resources outside modules in the mbp archive,
use `extra_files` instead.

[225]: https://github.com/maubot/maubot/issues/225
[abompard]: https://github.com/abompard

* Updated Pillow to 10.0.1.
* Updated Docker image to Alpine 3.18.
* Added logging for errors for /whoami errors when adding new bot accounts.
* Added support for using appservice tokens (including appservice encryption)
in standalone mode.

* Added `in_thread` parameter to `evt.reply()` and `evt.respond()`.
* By default, responses will go to the thread if the command is in a thread.
* By setting the flag to `True` or `False`, the plugin can force the response
to either be or not be in a thread.
* Fixed static files like the frontend app manifest not being served correctly.
* Fixed `self.loader.meta` not being available to plugins in standalone mode.
* Updated to mautrix-python v0.19.6.

* Dropped support for using a custom maubot API base path.
* The public URL can still have a path prefix, e.g. when using a reverse
proxy. Both the web interface and `mbc` CLI tool should work fine with
custom prefixes.
* Added `evt.redact()` as a shortcut for `self.client.redact(evt.room_id, evt.event_id)`.
* Fixed `mbc logs` command not working on Python 3.8+.
* Fixed saving plugin configs (broke in v0.3.0).
* Fixed SSO login using the wrong API path (probably broke in v0.3.0).
* Stopped using `cd` in the docker image's `mbc` wrapper to enable using
path-dependent commands like `mbc build` by mounting a directory.
* Updated Docker image to Alpine 3.17.

* Added encryption dependencies to standalone dockerfile.
* Fixed running without encryption dependencies installed.
* Removed unnecessary imports that broke on SQLAlchemy 1.4+.
* Removed unused alembic dependency.