feat: add DynamicTestsGeneratorIncrementalTests

[TimothyMakkison]

Add tests to verify that DynamicTestsGenerator uses incremental caching

[claude]

Code review

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

This PR adds solid incremental generator testing following the established patterns from other generator tests in the codebase. The changes correctly:

• Add tracking name constant for test observability
• Follow the same pipeline structure as MethodAssertionGenerator
• Verify all three key incremental scenarios (cache hit, modification, and new addition)
• Maintain consistency with existing incremental test patterns

The implementation aligns with TUnit's performance-first principle by ensuring the DynamicTestsGenerator properly leverages incremental compilation.