fmtlib/fmt

功能明確：實作 C++20 std::format、安全 printf、Dragonbox 浮點格式化與編譯期格式檢查，且有大量範例與測試。MIT 授權、無外部相依、跨平台，適合需要高效格式化的 C++ 專案；成熟度高。 Implements C++20 std::format, safe printf, Dragonbox float formatting, and compile-time checks with extensive examples and tests. MIT licensed, dependency-free, cross-platform; mature choice for performance-sensitive C++ projects.