Summary

Refactors pool_traits.h to:

• Use thread_concepts.h instead of duplicated concept definitions
• Remove conditional USE_STD_CONCEPTS preprocessor logic
• Replace std::enable_if with requires clauses where applicable

Parent Issue

Part of #271

Tasks

• Include thread_concepts.h
• Remove duplicated concept definitions (Callable, VoidCallable, etc.)
• Update template constraints to use concepts
• Maintain C++17 fallback compatibility if needed

Related Files

• include/kcenon/thread/core/pool_traits.h