Speed up TUnit.Engine.Tests in CI #7359

TUnit.Engine.Tests (Reflection mode) takes about 6.4 minutes on ubuntu and windows in the modularpipeline job (run 40786972231), and it sits on the job's critical path:

• RunEngineTestsModule depends on about 11 other test modules and holds NotInParallel("NetworkTests"), so it starts only after everything else has finished.
• Every engine test launches TUnit.TestProject as a child process. Each child gets --report-trx and --hangdump. Both extensions register Microsoft.Testing.Platform test-host controllers (TrxProcessLifetimeHandler, the hang-dump controller), so every child relaunches itself as a second process. Local medians on an empty filter: no flags 1.1 s, --report-trx 1.9 s, --hangdump about +0.7 s.

Plan:

1. Run the Reflection-mode engine tests in a job of their own, as the AOT-mode ones already are in aot.yml.
2. Drop --hangdump from child runs and bound them with --timeout, as the AOT path does.
3. Replace TRX as the child result source with an in-process reporter, adapted to the existing TestRun model so the assertions stay unchanged.