feat: add TUnit.Aspire package

[thomhurst]

Summary

• Adds TUnit.Aspire package with AspireFixture<TAppHost> that manages the full Aspire distributed app lifecycle (build, start, wait-for-resources, stop, dispose), eliminating ~50 lines of boilerplate per test project
• Supports direct use via [ClassDataSource<AspireFixture<Projects.MyAppHost>>] or subclassing with virtual hooks (ConfigureBuilder, WaitBehavior, ResourceTimeout, ResourcesToWaitFor, WaitForResourcesAsync)
• Includes WatchResourceLogs() for opt-in per-test resource log streaming
• Updates the TUnit.Aspire.Starter template to use the new package instead of raw Aspire.Hosting.Testing boilerplate

Closes #4768

Test plan

• Builds across all three TFMs (net8.0, net9.0, net10.0) with zero errors
• dotnet pack produces valid NuGet package
• Pipeline project builds with new Sourcy-generated reference
• CI passes
• Verify template compiles when instantiated with dotnet new tunit-aspire-starter

🤖 Generated with Claude Code

[claude]

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.

This PR introduces a well-designed TUnit.Aspire package that provides clean lifecycle integration for Aspire distributed app testing. The implementation follows TUnit patterns, uses appropriate async patterns (ValueTask for potentially-synchronous disposal), and significantly improves developer experience by eliminating ~50 lines of boilerplate per test project.

[claude]

Code review

No issues found. Checked for bugs and CLAUDE.md compliance.

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This PR introduces a well-designed package that significantly reduces boilerplate for Aspire testing. The implementation follows TUnit's patterns correctly:

• Lifecycle management through and is properly implemented
• Extensibility via virtual methods (, , etc.) provides good customization points
• Template updates correctly demonstrate usage patterns with the new fixture
• Code reduction is substantial (eliminates ~50 lines of boilerplate per test project)

The refactoring of the CloudShop example validates the approach in a real-world scenario, reducing the fixture from 48 to 29 lines while maintaining all functionality.