Allow arbitrary nesting order when using Annotated and NotRequired together

[latekvo]

As per python documentation, python allows usage of Annotated, NotRequired, ReadOnly, and other modifications in arbitrary nesting order.
As far as I see, this isn't documented anywhere, but LangGraph completely breaks when Annotated is not the outermost modifier:

class MyGoodState(TypedDict):
    foo_list: Annotated[NotRequired[str], operator.add]

class MyBadState(TypedDict):
    foo_list: NotRequired[Annotated[str, operator.add]]

Performing fan-in by appending to MyGoodState["foo_list"]:

No errors

Performing fan-in by appending to MyBadState["foo_list"]:

langgraph.errors.InvalidUpdateError: At key 'foo_list': Can receive only one value per step. Use an Annotated key to handle multiple values. For troubleshooting, visit: https://python.langchain.com/docs/troubleshooting/errors/INVALID_CONCURRENT_GRAPH_UPDATE

In the same documentation fragment i linked before, they acknowledge that some libraries may break, that's why I'm not opening this as an issue, but as a feature request.

[hinthornw]

cc @vbarda would be good to fix