The cached decorators always return a Deferred, which was not
properly propagated. It was close enough when wrapping coroutines,
but failed if a bare function was wrapped.
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
Cached functions accept an `on_invalidate` function, which we failed to add to the type signature. It's rarely used in the files that we have typed, which is why we haven't noticed it before.
