`defer.returnValue` was only needed in Python 2; in Python 3, a simple
`return` is fine.
`twisted.internet.defer.returnValue` is deprecated as of Twisted 24.7.0.
Most uses of `returnValue` in synapse were removed a while back; this
cleans up some remaining bits.
During the migration the automated script to update the copyright
headers accidentally got rid of some of the existing copyright lines.
Reinstate them.
Part of #9744
Removes all redundant `# -*- coding: utf-8 -*-` lines from files, as python 3 automatically reads source code as utf-8 now.
`Signed-off-by: Jonathan de Jong <jonathan@automatia.nl>`
- Update black version to the latest
- Run black auto formatting over the codebase
- Run autoformatting according to [`docs/code_style.md
`](80d6dc9783/docs/code_style.md)
- Update `code_style.md` docs around installing black to use the correct version
Run `isort`, `flake8` and `black` over the `contrib/` directory and `synctl` script. The latter was already being done in CI, but now the linting script does it too.
Fixes https://github.com/matrix-org/synapse/issues/7910
