`add_offset` and `scale_factor` attributes cause type promotion of the entire array

[gdkrmr]

julia> CFDiskArray(fill(1f0, 3, 3, 3), Dict("add_offset" => 0.0, "scale_factor" => 1.0)) |> eltype
Union{Missing, Float64}                                                                           

This is the reason for JuliaDataCubes/YAXArrays.jl#202

[gdkrmr]

struct CFDiskArray{T,N,MT,P,OT} <: AbstractDiskArray{T,N}
    a::P
    mv::MT
    add_offset::OT
    scale_factor::OT
end

is there a reason why mv can be different from eltype(a)?

[felixcremer]

Is this fixed by #16?