In #371, @saaketp reported:

The second problem is not clear whether it was intentional or a mistake. The actual type returned by the metadata function is a subclass of email.message.Message which supports "dict-like" operations like .get and .items(). I have seen some scripts rely on this dict-like behavior and I only noticed these methods are not present in PackageMetadata protocol because of pyright complaining.

Are those methods intentionally left out of the protocol or should they be added?