Support for typing.NotRequired

[giograno]

In #11 we shipped some support for non-total TypedDict. In our implementation, we extend the original type of every attribute with str. With this trick, the serialization layer can put a special marker for keys that are not present in the dictionary.

TypedDict also has the possibility to use typing.NotRequired to achieve something similar.
For instance:

class EngineParameter(TypedDict):
    type_: str
    given_value: NotRequired[str | None]

In this case, the given_value key can be omitted, and the typechecker won't raise any concern.
Transforming the class as follows won't be correct, since now type_ could be omitted, while it is not in the case in the original implementation.

class EngineParameter(TypedDict, total=False):
    type_: str
    given_value: str | None

This PR implements the support for typing.NotRequired with the same logic as #11.

Closes PNX-601

[bentsku]

LGTM, nice addition and nice find!

Here's the docs about the Required and NotRequired types: https://typing.python.org/en/latest/spec/typeddict.html#required-notrequired
Edit: and the PEP: https://peps.python.org/pep-0655/

Might be worth noting that total=False can also have Required, but let's not get stricter 😅

Only have a few comments nit, and a thought about the testing 👍 nice fix!