reduce tests
julia> A = Tensor(Dense(SparseList(Element(0.0))), [0.0 0.0 4.4; 1.1 0.0 0.0; 2.2 0.0 5.5; 3.3 0.0 0.0])
4×3 Tensor{DenseLevel{Int64, SparseListLevel{Int64, Vector{Int64}, Vector{Int64}, ElementLevel{0.0, Float64, Int64, Vector{Float64}}}}}:
 0.0  0.0  4.4
 1.1  0.0  0.0
 2.2  0.0  5.5
 3.3  0.0  0.0
julia> reduce(+, A, dims = (1,))
1×3 Tensor{DenseLevel{Int32, DenseLevel{Int32, ElementLevel{0.0, Float64, Int64, Vector{Float64}}}}}:
 6.6  0.0  9.9
julia> reduce(+, A, dims = 1)
1×3 Tensor{DenseLevel{Int32, DenseLevel{Int32, ElementLevel{0.0, Float64, Int64, Vector{Float64}}}}}:
 6.6  0.0  9.9
julia> reduce(+, A, dims = (2,))
4×1 Tensor{DenseLevel{Int32, DenseLevel{Int32, ElementLevel{0.0, Float64, Int64, Vector{Float64}}}}}:
 4.4
 1.1
 7.7
 3.3
julia> reduce(+, A, dims = 2)
4×1 Tensor{DenseLevel{Int32, DenseLevel{Int32, ElementLevel{0.0, Float64, Int64, Vector{Float64}}}}}:
 4.4
 1.1
 7.7
 3.3
julia> reduce(+, A, dims = (1, 2))
1×1 Tensor{DenseLevel{Int32, DenseLevel{Int32, ElementLevel{0.0, Float64, Int64, Vector{Float64}}}}}:
 16.5
julia> reduce(+, A, dims = (:))
16.5

