This commit also contains a related semantic change: it adds `Shape`
and `ShapeCastable` to the `__all__` list in `amaranth.hdl`. This is
consistent with the policy that is laid out in the new documentation,
which permits such additions without notice.
Co-authored-by: mcclure <mcclure@users.noreply.github.com>
Because `importlib.metadata.PackageNotFoundError` inherits from
`ImportError`, the code did not previously work in the way that was
stated in the comment. We should probably deprecate `__version__`
entirely at some point.
