Support for PEP 604 (Allow writing union types as X | Y) with "<type> | None" as Optional

[xlorepdarkhelm]

PEP 604, which was implemented in Python 3.10, allows for unions to be specified through using the pipe (union) operator. As the Optional[<type>] type already is essentially a shortcut for Union[<type>,None], the new implementation also means that Union[<type>, None] is able to be written as <type> | None. This confuses desert right now and it fails to be able to make a schema.

The current work-around is to still use the Optional[<type>] syntax, which involves importing Optional from typing. It would be nice if desert was more flexible for this.