Missing `similar` implem

[gdalle]

Here's an MWE on Metal but the same goes for CUDA: similar goes back to CPU Array.

julia> using Adapt, DeviceSparseArrays, Metal, SparseArrays

julia> A = adapt(MtlArray, DeviceSparseMatrixCSR(sprand(Float32, 10, 10, 0.1)));

julia> typeof(similar(A, 10))
Vector{Float32} (alias for Array{Float32, 1})