Import typeddict from typing_extentions

[eavanvalkenburg]

Description of the change

When using classes from the types with Pydantic [as mentioned here],(https://docs.pydantic.dev/2.1/usage/types/dicts_mapping/#typeddict) Pydantic throws an error that typeddict needs to come from typing_extentions for python < 3.11, hence this PR.

Motivation

Allows this packages classes to be used within pydantic based classes.

Type of change

Choose one: Bug Fix for #102

Checklist

• I have performed a self-review of my code.
• I have added detailed comments to my code where applicable.
• I have verified that my change does not break existing code.
• My PR is based on the latest changes of the main branch (if unsure, please run git pull --rebase upstream main).
• I am familiar with the Google Style Guide for the language I have coded in.
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[markmcd]

Do you have a link that explains why it's needed? The link you provided lists:

This is a new feature of the Python standard library as of Python 3.8. Prior to Python 3.8, it requires the typing-extensions package. But required and optional fields are properly differentiated only since Python 3.9. We therefore recommend using typing-extensions with Python 3.8 as well.

We only support 3.9+, so it sounds like it's already OK, but that obviously isn't your experience so I'd like to understand the problem better.

[eavanvalkenburg]

@markmcd this is where they go into the details of this choice, I also do not like it, but would love to use the direct types in a pydantic class, hence this issue!

[MarkDaoust]

This looks pretty reasonable.

The tests only pass because typing_extensions is indirectly pulled in by our [dev] install.

Before we merge this, we need to add typing-extensions to the requirements in setup.py.

Optional: use environment markers to make it a conditional requirement.

[MarkDaoust]

To keep things simple is there any downside to always importing from typing-extensions?

I think I'm going to start with that.