Refactor AppTestHelper to use RunAsync

[Copilot]

Fixes

Proposed Changes/Todos

AppTestHelper could hang or swallow failures because it ran apps with blocking Run plus separate timeout handling. This refactors the helper to rely on IApplication.RunAsync cancellation semantics.

• Use IApplication.RunAsync with the helper’s linked cancellation token
• Ensure runnable and application cleanup runs even when RunAsync completes as canceled
• Make WaitIteration observe timeout/hard-stop cancellation
• Preserve and rethrow UI-thread action exceptions
• Add focused integration coverage for post-startup cancellation and action failure propagation
• Update quit-key coverage to assert after stop propagation

Pull Request checklist:

• I've named my PR in the form of "Fixes #issue. Terse description."
• My code follows the style guidelines of Terminal.Gui - if you use Visual Studio, hit CTRL-K-D to automatically reformat your files before committing.
• My code follows the Terminal.Gui library design guidelines
• I ran dotnet test before commit
• I have made corresponding changes to the API documentation (using /// style comments)
• My changes generate no new warnings
• I have checked my code and corrected any poor grammar or misspellings
• I conducted basic QA to assure all features are working

[Copilot]

Pull request overview

This PR refactors the integration test AppTestHelper to run applications through IApplication.RunAsync, improving cancellation behavior and exception propagation in fluent UI tests.

Changes:

• Adds configurable helper timeouts through With.A(...).
• Switches app execution to RunAsync with the helper’s linked cancellation token.
• Adds focused tests for timeout shutdown, action exception propagation, and quit-key stop propagation.

Reviewed changes

Copilot reviewed 4 out of 4 changed files in this pull request and generated 2 comments.

File	Description
Tests/AppTestHelpers/AppTestHelper.cs	Refactors background app execution and WaitIteration exception/cancellation handling.
Tests/AppTestHelpers/With.cs	Adds optional timeout forwarding to helper factory methods.
Tests/IntegrationTests/FluentTests/TestContextTests.cs	Adds coverage for timeout-driven shutdown and action exception propagation.
Tests/IntegrationTests/FluentTests/TestContextKeyEventTests.cs	Updates quit-key test to wait for stop propagation.

[tig]

@copilot see CR feedback and addrss.

[tig]

@copilot see CR feedback and address.

[tig]

@copilot see CR feedback and address.

[Copilot]

@copilot see CR feedback and addrss.

Addressed the CR feedback in e4a7ca8: RunAsync cleanup now happens in a finally path, and the cancellation test now cancels after helper startup instead of using a tiny startup timeout.

[Copilot]

@copilot see CR feedback and address.

Already addressed in e4a7ca8: RunAsync cleanup is now in a finally path, and the cancellation test cancels after helper startup instead of using a tiny startup timeout.

@copilot see CR feedback and address.

Already addressed in e4a7ca8: RunAsync cleanup is now in a finally path, and the cancellation test cancels after helper startup instead of using a tiny startup timeout.