Fix mypy and line-too-long errors

[fritzo]

This fixes two errors I was seeing on Python 3.8.11 and Python 3.11.4:

1. A mypy error

    @functools.wraps(fn)
    def _fn(
        *args: _P.args,
        name: Optional[str] = None,
        infer: Optional[InferDict] = None,
        obs: Optional[_T] = None,
        **kwargs: _P.kwargs,
    ) -> Optional[_T]:
        is_observed = obs is not None

        if not am_i_wrapped():
            return fn(*args, **kwargs)
        else:
>           msg = Message[_P, _T](
                type=type,
                name=name,
                fn=fn,
                is_observed=is_observed,
                args=args,
                kwargs=kwargs,
                value=obs,
                scale=1.0,
                mask=None,
                cond_indep_stack=(),
                done=False,
                stop=False,
                continuation=None,
                infer=infer if infer is not None else {},
            )
E           TypeError: '_TypedDictMeta' object is not subscriptable

../../pyro-ppl/pyro/pyro/poutine/runtime.py:354: TypeError

2. A ruff line too long error

ruff check .
pyro/poutine/indep_messenger.py:29:121: E501 Line too long (129 > 120 characters)