Refactor benchmarks to use typed enums for engine/mode
Replaced string-based identifiers for serializer engine, I/O mode, and dispatch mode with strongly-typed enums (BenchmarkEngine, BenchmarkIoMode, BenchmarkDispatchMode). Added BenchmarkEnums.cs with ToDisplay() helpers for consistent output. Updated all benchmark implementations, DTOs, and output logic to use enums. Removed obsolete string constants from Configuration.cs. Merged allocation measurement methods in BenchmarkLoop.cs for clarity. Improves type safety, maintainability, and output consistency.
Refactor: extract serializer benchmarks to separate files
Moved AcBinary, MemoryPack, MessagePack, and SystemTextJson benchmark classes into dedicated files for clarity. Centralized options formatting and MemoryPack selection logic in a new BenchmarkOptions helper. Updated Program.cs to use these helpers and removed redundant inline implementations, improving code organization without changing benchmark logic.