typing: widget: Add typed widget outputs and JSON shapes.

[aryan98795]

Define TypedDicts for todo/poll widget outputs and JSON payloads. Update widget processing to use typed structures and casts. Update widget rendering to use the new return shape. Add a widget test fixture and normalize submessages in tests.

Fixes: #1576

External discussion & connections

• Discussed in #zulip-terminal in topic
• Fully fixes #
• Partially fixes issue #
• Builds upon previous unmerged work in PR #
• Is a follow-up to work in PR #
• Requires merge of PR #
• Merge will enable work on #

How did you test this?

• Manually - Behavioral changes
• Adapting existing automated tests
• Manually - Visual changes
• Adding automated tests for new behavior (or missing tests)
• Existing automated tests should already cover this (only a refactor of tested code)

Self-review checklist for each commit

• It is a minimal coherent idea
• It has a commit summary following the documented style (title & body)
• It has a commit summary describing the motivation and reasoning for the change
• It individually passes linting and tests
• It contains test additions for any new behavior
• It flows clearly from a previous branch commit, and/or prepares for the next commit

[zulipbot]

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

[Copilot]

Pull request overview

Adds stronger typing around widget (submessage) payloads and processing results, and updates widget rendering/tests to use the new structured return shapes.

Changes:

• Define TypedDict types for submessages and poll/todo widget payloads/results.
• Update process_todo_widget / process_poll_widget to return typed dict “result objects” instead of tuples.
• Update message rendering and widget unit tests to consume the new result shape.

Reviewed changes

Copilot reviewed 5 out of 5 changed files in this pull request and generated 2 comments.

Show a summary per file

File	Description
zulipterminal/widget.py	Switch widget processors to typed result dicts and import shared widget/submessage types.
zulipterminal/ui_tools/messages.py	Update widget rendering to use the new {title,tasks} / {question,options} result shapes.
zulipterminal/model.py	Normalize stored submessage schema (use id, drop type/submessage_id).
zulipterminal/api_types.py	Add TypedDict definitions for submessages and poll/todo widget structures; tighten Message.submessages typing.
tests/widget/test_widget.py	Update widget tests to assert on new result dict shapes and use shared api_types types.

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