`std::formatter` specialization

Please provide a `std::formatter` specialization similar to the one `std::stacktrace` provides:

https://godbolt.org/z/x3zKn6vfn

```
terminate called after throwing an instance of 'RuntimeError'
what(): Encountered error code: 139
0# RuntimeError::RuntimeError(std::basic_format_string::type>, int&&) at /app/example.cpp:16
1# h() at /app/example.cpp:23
2# g() at /app/example.cpp:28
3# f() at /app/example.cpp:33
4# main at /app/example.cpp:38
5# at :0
6# __libc_start_main at :0
7# _start at :0
8#
```

从链接的 Compiler Explorer 示例开始，将其当前输出与 std::stacktrace 提供的格式化行为进行比较。追踪库中现有的 stacktrace 格式化入口点，然后验证 std::formatter 特化能够为该示例生成等效的格式化输出。

由索引模型根据 Issue 内容生成。