Bare Callable doesn't get picked up by extension

[dhermes]

i.e. Callable as standalone:

    Args:
        target_mesh (~galerkin_reconstruction.Mesh): A mesh which is covered
            by a ``donor_mesh``.
        donor_mesh (~galerkin_reconstruction.Mesh): A mesh, presumably of the
            same degree as ``target_mesh``.
        intersect_callback (Callable): Hi Jon this is the issue
        start_index (Optional[int]): The surface element index to start the
            search with. Defaults to ``0``.

yields

while

        intersect_callback (Callable[float]): Hi Jon this is the issue

yields

[theacodes]

Callable is typically not supposed to be bare, yeah?

[dhermes]

Don't know.

[theacodes]

(insert shruggie here)

[dhermes]

From docs:

A plain Callable is equivalent to Callable[..., Any], and in turn to collections.abc.Callable.