Refactor benchmark suite to use enums for config
Replaced string parameters for layer, opMode, and serializerMode with strongly-typed enums (BenchmarkLayer, BenchmarkOpMode, SerializerSelectionMode) across BenchmarkLoop, Menu, and Program. Updated CLI parsing and menu logic to use Enum.TryParse and return enums. Added XML docs for new enums. Improves type safety, code clarity, and maintainability.