Support of extra and not required arguments for TypedDict in JSON schema generator

[tokarenko]

I am tring to generate JSON schema for TypedDict allowing for extra/optional arguments. With NotRequired typing I get the following error:

from typing import TypedDict
from apischema.json_schema import deserialization_schema

class MyTypedDict(TypedDict):
    my_key1: Optional[int]
    my_key2: NotRequired[int]

deserialization_schema(MyTypedDict)
>>> TypeError: NotRequired accepts only a single type. Got (<class 'int'>,).

Workaround with total=False seems to work but I expect additionalProperties to be True instead of False.

from typing import TypedDict, List
from apischema.json_schema import deserialization_schema

class MyTypedDict(TypedDict, total=False):
    a: str
    b: str

deserialization_schema(MyTypedDict)
>>> {'type': 'object', 'properties': {'a': {'type': 'string'}, 'b': {'type': 'string'}}, 'additionalProperties': False, '$schema': 'http://json-schema.org/draft/2020-12/schema#'}

I suggest the following:

1. Add support for PEP 728 closed class parameter as a way to enable "additionalProperties": true in JSON schema for TypedDict.
2. Set "additionalProperties": true by default for TypedDict as the PEP states:

Passing closed=False explicitly requests the default TypedDict behavior, where arbitrary other keys may be present ...