feat: add archived status to todos and issues

[franccesco]

Summary

Adds archived field to Todo, IssueDetails, and IssueListItem models so SDK users can identify archived items. Previously, only Goals and Headlines exposed archive status.

• Todos: The API doesn't return an explicit Archived key — instead, a non-null CloseTime indicates the todo is archived. A new IsPresent annotated type coerces this datetime into a clean archived: bool field on the model.
• Issues: The API returns Archived: true/false directly. Added it to IssueDetails and IssueListItem models, wired through the issues transform mixin.

Changes

• Add IsPresent reusable annotated type for coercing nullable values to booleans
• Add archived field to Todo model (derived from API's CloseTime)
• Add archived field to IssueDetails and IssueListItem models
• Update issues transform mixin to pass through Archived from API responses
• Include CloseTime: None in todo create payloads for correct default
• Update test fixtures and inline test data with new fields

Test plan

• All 442 unit tests passing
• 0 basedpyright errors
• ruff lint and format clean
• Verify against live API that archived returns expected values for todos and issues

🤖 Generated with Claude Code