Add unit and type stability tests #114
Description
We should add tests similar to the ones in https://github.com/trixi-framework/Trixi.jl/blob/main/test/test_type.jl and https://github.com/trixi-framework/Trixi.jl/blob/main/test/test_unit.jl (fluxes with the same argument twice) to TrixiAtmo.jl.