Improve typing & test approach for widgets

[neiljp]

Following up on earlier work on polls and todo widget handling in messages, this could involve:

• [ ] Use TypedDict (or dataclass) for the result of process_todo_widget (and for polls) instead of a nested dict with a union.
• [ ] Consider if the extracted JSON should match specific types, that we can define using TypedDict or similar too.
• [ ] Consider factory fixtures for the Submessage content in tests.
• [ ] Move Submessage into api_types.py, and use it to improve the definition of Message.

See # zulip-terminal > Widget followup work for the original listing of these points and for followup discussion. These points arose in earlier work on widget implementation, so you might read those PRs to understand the background further.

[zulipbot]

Hello @zulip/server-refactoring members, this issue was labeled with the "area: refactoring" label, so you may want to check it out!

[ellikamishra]

I would like to work on this issue.

[apoorvapendse]

Hey @ellikamishra, you can claim the issue using @zulipbot claim Checkout this section of the contributing guide for more info.

[ellikamishra]

@zulipbot claim

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[Gopinath-Mahendiran]

@ellikamishra are you working on this ?

[ellikamishra]

@ellikamishra are you working on this ?

Yes

[Subham-KRLX]

Hi @neiljp and @ellikamishra, I’m also interested in working on this issue as part of my GSoC and Zulip open-source contribution journey.

If ellikamishra is no longer actively working on this, I’d love to take over or collaborate. Please let me know if that would be okay — I’ve gone through the related discussions and PR,s and would be excited to help move this forward.

Thanks!