feat: improve the code sample for std::inplace_vector

[YukunJ]

Brief: improve the code sample for std::inplace_vector section.

Since the tutorial is explicitly mentioning

a.

最讨喜的一个性质是：当 T 是 trivially copyable 时，inplace_vector<T, N> 本身也是 trivially copyable
doc: https://cppreference.com/cpp/container/inplace_vector/try_push_back

b.

容量超限时的行为也设计得克制：push_back 超过 N 会抛 std::bad_alloc（异常关闭时退化为 terminate），而想避免异常可以用 C++26 的 try_push_back/try_emplace_back，它们超限时不抛、返回一个错误指示，适合 -fno-exceptions 环境。

It's worthwhile to show these two points in the code sample.

QA:
see godbolt link https://godbolt.org/z/K78EnTnYM

BTW:

I locally tested that, it seems like the memory footprint of std::inplace_vector is N * sizeof(T) + size_t, aka the raw underlying storage plus a size. But I wasn't sure if all standard implementation follows this convention. If you can find the cpp reference for this, feel free to add this point to the tutorial as well.

sizeof(std::inplace_vector<int, 4>>) = 20
sizeof(std::inplace_vector<int, 6>>) = 28
sizeof(std::inplace_vector<int, 11>>) = 48

@Charliechen114514

[Charliechen114514]

感谢改进！我确认了下代码没问题的！

sizeof 那条 BTW —— 查了 C++26 标准草案和再次确认cppreference, 确实没有依据,不建议加进教程。 我稍微确认了下，不管是cppreference还是C++标准草案，的确没有标准定义，找到最相近的是下面的这个

[inplace.vector.overview] §1 对布局的全部规定只有这句(见 https://eel.is/c++draft/inplace.vector.overview ):

An inplace_vector is a contiguous container. Its capacity is fixed and its elements are stored within the inplace_vector object itself.

cppreference也只是在inplace_vector最上面提到：

std::inplace_vector is a dynamically-resizable array with contiguous inplace storage. The elements of type T are stored and properly aligned within the object itself. The capacity of the internal storage is fixed at compile-time and is equal to N.

即标准只保证「连续容器 + 容量固定 + 元素存在对象自身内部」,似乎没有提到 sizeof / 对象总大小 / size 字段表示的任何规定。您测出来的 N * sizeof(T) + size_t(20/28/48)是 libstdc++/libc++ 的实现布局, —— 看起来应该属于实现定义,不是标准约定。所以的话，可能会将教程后续优化为「主流实现常见布局」的脚注式备注。

最后感谢您对本教程的持续贡献和关注！