Adds Uno.WinUI and DryIoc.Uno.WinUI unit tests

[dansiegel]

Description of Change

This pull request introduces comprehensive unit test projects for Prism.Uno.WinUI and Prism.DryIoc.Uno.WinUI. These tests validate core functionalities, including:

• Container Integration: Verifying DryIoc container extension and framework exception registration.
• API Contract: Ensuring public types and members are discoverable and loadable.
• Region Management: Covering RegionManager, Region, and NavigationViewRegionAdapter behaviors, including adding/removing regions, context changes, and navigation requests.
• Dialogs and Interactivity: Testing DialogService, IDialogWindow contracts, and InvokeCommandAction properties.
• Application Lifecycle: Validating PrismApplicationBase and PrismApplication extensibility points.
• Utility APIs: Confirming expected behavior of internal utility types.

The changes also update the CI/CD workflows (build_uno.yml and ci.yml) to enable the execution of these new unit tests, improving test coverage and ensuring stability for Prism on the Uno Platform. The coverlet.msbuild package is also added to Directory.Packages.props to support code coverage analysis for these new tests.

Bugs Fixed

• None

API Changes

None

Behavioral Changes

None

PR Checklist

• Has tests (if omitted, state reason in description)
• Rebased on top of master at time of PR
• Changes adhere to coding standard