Fix: 2 typos in variant section

[YukunJ]

Brief: Fix 2 typos in std::variant section.

1. int type usually takes 4 bytes on 64 bit architectures.
2. std::variant<int, std::string> would take 8 (sizeof(size_t)) + 32 (max(sizeof(int), sizeof(std::string)) storage space then.

Please refer to this for reproduction: https://godbolt.org/z/sbvEMW56G

@Charliechen114514

[Charliechen114514]

Review：

1. Yes, I Do make a typo in std::variant section at line 435, at least cpp reference page siting at: https://en.cppreference.com/cpp/language/types, int is at least 16 bits(2 bytes) at platform LP32.
2. Verified in both godbolt and my local machine, which is

Item	Environment
Operating System	Arch Linux x86_64 on WSL2
Kernel	6.6.114.1-microsoft-standard-WSL2
Compiler	GCC 16.1.1
C++ Standard	C++17 (-std=c++17)
Architecture	x86_64, LP64 ABI

Much more appreciate for your help!

审查了以下，的确又搞低级错误了（手动捂脸哭笑

1. Line 435的确搞错了，因为手册来不及翻，找了下https://en.cppreference.com/cpp/language/types，的确int规定的是最小2字节，其他平台4字节。
2. 修改正确，自己在godbolt和自己如下环境的本地验证通过

项目	环境
操作系统	Arch Linux x86_64，运行于 WSL2
内核版本	6.6.114.1-microsoft-standard-WSL2
编译器	GCC 16.1.1
C++ 标准	C++17（-std=c++17）
体系结构	x86_64，LP64 ABI

非常感激您的认真阅读和勘误！