cosmo_array multiplication does not return cosmo_array

[bwvdnbro]

Merging #137 and #141 unfortunately broke some of the visualisation functions. Consider the following code snippet:

data.gas.HI_mass_fraction = (
    data.gas.masses
    * data.gas.element_mass_fractions.hydrogen
    * data.gas.species_fractions.HI
)
HI_map = project_gas(
                    data,
                    resolution=8000,
                    project="HI_mass_fraction",
                )

All the data.gas.XXX attributes are cosmo_arrays, but unfortunately data.gas.HI_mass_fraction is not, since multiplication of cosmo_arrays does not conserve the cosmo properties. project_gas will fail when it tries to confirm that HI_mass_fraction and the coordinates are compatible cosmological quantities.

The only way to fix this would be to add support for multiplication (and maybe some other operators) to cosmo_array. We probably also want to disable unsupported operations to be on the safe side.

[kyleaoman]

#131 is a symptom of the same issue. #132 is nearly ready to merge and will implement all the ufuncs supported for unyt_arrays for use with cosmo_arrays.