…meral

Previously, if a RoomStreamToken object were provided, new_token would
be set to `None`. In the same changeset, which was intended to prevent
mypy from failing, `_notify_app_services_ephemeral` was configured
to allow `new_token` to be an Optional[int]
(559974f).

However, if `None` is provided, `_notify_app_services_ephemeral` will
end up passing `None` to `set_type_stream_id_for_appservice`, which will
effectively clear each appservice's stream token for the given
`stream_key`. This seems like a bug to do every time we have a
RoomStreamToken rather than an int.

Instead, I'm converting the RoomStreamToken to an int using
RoomStreamToken.stream. I think this is the right way to convert to an
int. If RoomStreamToken this ends up being a vector clock, `stream` will
be the minimum stream token amongst all workers... which I think is fine?

…_as_room_stream_token

While searching around for all types that were eventually passed into on_new_event,
I found a couple methods which didn't specify the type they returned. So this commit
adds return type hints for those methods.

I didn't do any other arguments as I plan to type-hint those files later anyways.

…instead

This is a small effort to reduce the layers of methods we have here.

Also, I've opted to continue converting the RoomStreamToken to an int,
but only for when tracking stream tokens of EDUs. As stated in the
comment, this shouldn't have any gaps as long as we *always* convert to
minimum value.

…_as_room_stream_token

Co-authored-by: Richard van der Hoff <1389908+richvdh@users.noreply.github.com>