[WIP] Use an explicit Result type instead of exceptions for data errors

[Malcohol]

I'm starting to look into shared libraries and these tend not to get on well with exceptions. In particular, throwing an exception across a shared library boundary can lead to issues.

As it happens, most of the scenarios where I use exceptions are not "exceptional", just bad data. Consequently, it's quite reasonable to handle errors explicitly rather than implicitly in these cases. (Note that I'm not ideological either way about exceptions. It's the practical problem that primarily motivates this change.)

I've improved the Result type (defined in terms of std::expected) and I'm shifting the APIs to use that instead.

I've upgraded the C++ standard to C++23, because it introduced std::expected.