fix(case): more explicit None defaults

[whitdog47]

This PR continues the previousl efforts to make None defaults and type conversions more explicit.

• In interactive.py, we found a few more explicit int() conversions needed for project and entity identifier fields.
• In the case severity and priority models, explicit default values (i.e. “= None”) have been added for optional fields.
• In the case models, explicit defaults have been set for multiple fields to improve clarity and consistency.

[Copilot]

Pull Request Overview

This PR aims to make None defaults and type conversions more explicit.

• In interactive.py, explicit int() conversions are introduced for project and entity identifier fields.
• In the case severity and priority models, explicit default values (i.e. “= None”) have been added for optional fields.
• In the case models, explicit defaults have been set for multiple fields to improve clarity and consistency.

Reviewed Changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated no comments.

File	Description
src/dispatch/plugins/dispatch_slack/case/interactive.py	Added explicit int() conversions for project and engagement IDs as well as entity ids.
src/dispatch/case/severity/models.py	Set explicit default values for optional fields in Pydantic models.
src/dispatch/case/priority/models.py	Assigned explicit defaults for optional fields and formatted the default_listener_doc for clarity.
src/dispatch/case/models.py	Introduced explicit default assignments for optional fields in various Pydantic models.

[wssheldon]

I'm assuming anything that was Optional without a default before (or with it I suppose) that was updated to * | None must now set a default of None?

Does this get all of them?

[whitdog47]

@wssheldon turns out there were 31 more files that needed it!