Introduce get_thermal_expansion_output() function

[jan-janssen]

Remove the code duplication of defining multiple instances of the ThermalExpansionOutput by defining one function to create the corresponding output object:

def get_thermal_expansion_output(temperatures_lst, volumes_lst, output_keys):
    return OutputThermalExpansion(
        **{
            k: getattr(ThermalExpansionProperties, k)
            for k in OutputThermalExpansion.fields()
        }
    ).get(
        ThermalExpansionProperties(
            temperatures_lst=temperatures_lst, volumes_lst=volumes_lst
        ),
        *output_keys,
    )

EDIT: syntax highlighting

Again this change was initially introduced in #176 and is now moved to a separate pull request.

[liamhuber]

One can do this, and the reduction of code duplication is indeed helpful, but I am sad that both OutputThermalExpansionProperties and OutputThermalExpansion both exist. The underlying symptom is that we're shoe-horning in an intermediate engine where no engine is necessary, because the dataclasses+callable infrastructure was conceived only in the context of lammps/ase/etc engines holding data. Still, might as well merge this as it at least makes the bad thing better.

[jan-janssen]

..., but I am sad that both OutputThermalExpansionProperties and OutputThermalExpansion both exist.

I agree, as discussed in the meeting today, I am open for suggestions, I just want to merge the parts we can agree on, to simplify future discussions.

... Still, might as well merge this as it at least makes the bad thing better.

Ok.