[ARTS3] Mocking scattering data interface.

[simonpf]

This PR aims to sketch out the ARTS integration of the new scattering data handling.

[simonpf]

@riclarsson As per out discussion from last week, I started replacing ParticulatePropertyTag with ScatteringSpeciesProperty as defined in src/core/scattering/properties.h. Could you have a look a that as well as the changes in atm.h? Thanks!

[riclarsson]

Nice!

Two things. The first serious, the second a minor design choice (that also has a bug).

The big problem first:
How does scattering, the CMake library, depend on artscore? I really think it is a bad idea to do this. We want less cross-dependencies to make all this work nicely in the end. (At some point, artscore might also depend on scattering since we want some internal functionality using multiple parts of core ARTS functionality. So it is expected to cross-pollinate, which could cause issues.)

The second minor thing:
I think there's a bug in ParticulateProperty toParticulatePropertyEnumOrThrow(const std::string_view x); The .cc file defines ParticulateProperty toParticulatePropertyOrThrow(std::string x);. The ENUMCLASS macro gives you ParticulateProperty toParticulatePropertyOrThrow(const std::string_view x); already. For SpeciesEnum, we also want short names, like you have in the .cc file. We definitely want short-names for SpeciesEnum, but are they really a requirement here? (Several people of RTE community will much more easily recognize C2H2 than Acetylene, but I cannot make C2H2 the enum name because we must support things like NO+, which isn't a good variable name [and workarounds like NOplus will add more confusion]. I do not see this as such a big deal in the ParticulateProperty enum, at least not with the names you have there today.)

[riclarsson]

constexpr auto operator<=>(const ScatteringSpeciesProperty& other) const = default;

[riclarsson]

@simonpf This does not compile so merging main arts3-dev is not good. There seems to be some problems with duplicate psd.cc files. We have to hold merging until we can compile it. (Or we will probably introduce even greater bugs.)

[simonpf]

So, this should in principle build. Could you add fftw3 to the build environment @olemke ?