* Deal with mypy errors w/ type-hinted pynacl 1.5.0

Fixes #11644.

I really don't like that we're monkey patching pynacl SignedKey
instances with alg and version objects. But I'm too scared to make the
changes necessary right now.

(Ideally I would replace `signedjson.types.SingingKey` with a runtime class which
wraps or inherits from `nacl.signing.SigningKey`.) C.f. https://github.com/matrix-org/python-signedjson/issues/16

* Deal with mypy errors w/ type-hinted pynacl 1.5.0

Fixes #11644.

I really don't like that we're monkey patching pynacl SignedKey
instances with alg and version objects. But I'm too scared to make the
changes necessary right now.

(Ideally I would replace `signedjson.types.SingingKey` with a runtime class which
wraps or inherits from `nacl.signing.SigningKey`.) C.f. https://github.com/matrix-org/python-signedjson/issues/16

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&gt;`>

... and use it in places where it's trivial to do so.

This will make it easier to pass room versions into the FrozenEvent
constructors.

Another signing test vector using an 'm.room.message' with content, so that the implementation will have to redact it