Add expected handling for safe_int class

[PLGCesar]

Minor error fixed.
Log:

Error: no template named 'expected' in namespace 'std'
46 |         std::expected<T, bad_safe_int> expected() const {
|         ~~~~~^
../../apps/mlibc/subprojects/frigg/include/frg/safe_int.hpp:51:7: error: no template named 'expected' in namespace 'std'
51 |         std::expected<T, E> or_unexpected(E error) const {
|         ~~~~~^
../../apps/mlibc/subprojects/frigg/include/frg/safe_int.hpp:53:16: error: no member named 'unexpected' in namespace 'std'
53 |                         return std::unexpected{error};
|                                ~~~~~^
../../apps/mlibc/subprojects/frigg/include/frg/safe_int.hpp:53:26: error: expected ';' after return statement
53 |                         return std::unexpected{error};
|                                               ^
|                                               ;
4 errors generated

I think it's all sorted out; CI compiled everything without errors at least.

[ArsenArsen]

this is probably okay but please clean up the commits

[PLGCesar]

Provavelmente está tudo bem, mas por favor, limpe os commits
Okay

[PLGCesar]

Provavelmente está tudo bem, mas por favor, limpe os commits.

Done

[no92]

Checking FTMs is fine, but why would std:: expected be missing in the first place if the header inclusion doesn't fail? Is it some old C++ standard being used?

[PLGCesar]

Verificar as FTMs é aceitável, mas por que std::expected estaria ausente se a inclusão do cabeçalho não falhou? Será que estão usando algum padrão antigo do C++?

Well, no old version of C++ is being used (besides, I tested it with C++23 and C++26) And the same error persists; I really don't get it, even including the file, it still doesn't seem exist

[ArsenArsen]

Checking FTMs is fine, but why would std:: expected be missing in the first place if the header inclusion doesn't fail? Is it some old C++ standard being used?

clang (at least up to some version) doesn't implement a requisite feature of concepts (IIRC) so the header exists but is effectively empty.

https://gcc.gnu.org/cgit/gcc/tree/libstdc++-v3/include/bits/version.def#n1598