This PR adds comprehensive MSTest support to skUnit, demonstrating that the framework is truly test-framework agnostic. Previously, all documentation and samples used xUnit exclusively, which could mislead users into thinking skUnit had a dependency on xUnit.

What's Changed

🆕 New Demo Project: Demo.MSTest

• Complete working MSTest project showing all key patterns
• Demonstrates [TestClass], [TestMethod], [DataTestMethod], and [ClassInitialize] attributes
• Shows proper TestContext.WriteLine integration for test output
• Includes sample scenarios for semantic, JSON, and basic chat testing

📖 Enhanced Documentation

• Updated README.md with side-by-side examples comparing xUnit, MSTest, and NUnit
• New docs/test-framework-integration.md - comprehensive guide covering all three major test frameworks
• Updated demos/README.md to include the new MSTest demo

🧪 Framework Comparison Examples

The new documentation shows how the same test looks across frameworks:

xUnit:

[Fact]
public async Task TestGreeting()
{
    await _scenarioAssert.PassAsync(scenarios, _chatClient);
}

MSTest:

[TestMethod] 
public async Task TestGreeting()
{
    await ScenarioAssert.PassAsync(scenarios, _chatClient);
}

The documentation examples now correctly include the required chatClient parameter in all PassAsync calls and follow best practices by reusing ScenarioAssert instances rather than creating them per test.

Why This Matters

This change proves that skUnit's architecture is genuinely framework-agnostic. The core skUnit library has zero dependencies on test frameworks - it only depends on Microsoft.Extensions.AI, SemanticKernel.Abstractions, and Markdig. Users can now confidently choose their preferred test framework without worrying about compatibility.

Validation

• ✅ All existing tests pass - zero breaking changes
• ✅ New demo project builds and discovers tests correctly
• ✅ Documentation examples are syntactically correct and match working code
• ✅ Code formatting follows project standards

Fixes #37.

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