Unify error handling

[Guekka]

Most components use expected for error handling: nif, tex... But common sometimes uses exceptions, in filesystem and strings And bsa is the worst of all, sometimes using both or just raw errors (beware of the dreaded std::vector<std::pair<Path, std::string>>. Can you guess that represents an error?)

[Guekka]

With the previous work, the situation has already gotten better. But we need more work. In particular, making all functions noexcept and replacing bool returns with proper errors