chunkmask tests
julia> A = Tensor(Dense(Dense(Element(0.0))), 15, 3)
15×3-Tensor
└─ Dense [:,1:3]
   ├─ [:, 1]: Dense [1:15]
   │  ├─ [1]: 0.0
   │  ├─ [2]: 0.0
   │  ├─ ⋮
   │  ├─ [14]: 0.0
   │  └─ [15]: 0.0
   ├─ [:, 2]: Dense [1:15]
   │  ├─ [1]: 0.0
   │  ├─ [2]: 0.0
   │  ├─ ⋮
   │  ├─ [14]: 0.0
   │  └─ [15]: 0.0
   └─ [:, 3]: Dense [1:15]
      ├─ [1]: 0.0
      ├─ [2]: 0.0
      ├─ ⋮
      ├─ [14]: 0.0
      └─ [15]: 0.0

julia> @finch begin
        let m = Finch.chunkmask(5, 1:15)
            for i = _
                for j = _
                    A[j, i] = m[j, i]
                end
            end
        end
    end
NamedTuple()
julia> AsArray(A)
15×3 Tensor{DenseLevel{Int64, DenseLevel{Int64, ElementLevel{0.0, Float64, Int64, Vector{Float64}}}}}:
 1.0  0.0  0.0
 1.0  0.0  0.0
 1.0  0.0  0.0
 1.0  0.0  0.0
 1.0  0.0  0.0
 0.0  1.0  0.0
 0.0  1.0  0.0
 0.0  1.0  0.0
 0.0  1.0  0.0
 0.0  1.0  0.0
 0.0  0.0  1.0
 0.0  0.0  1.0
 0.0  0.0  1.0
 0.0  0.0  1.0
 0.0  0.0  1.0
julia> A = Tensor(Dense(Dense(Element(0.0))), 14, 3)
14×3-Tensor
└─ Dense [:,1:3]
   ├─ [:, 1]: Dense [1:14]
   │  ├─ [1]: 0.0
   │  ├─ [2]: 0.0
   │  ├─ ⋮
   │  ├─ [13]: 0.0
   │  └─ [14]: 0.0
   ├─ [:, 2]: Dense [1:14]
   │  ├─ [1]: 0.0
   │  ├─ [2]: 0.0
   │  ├─ ⋮
   │  ├─ [13]: 0.0
   │  └─ [14]: 0.0
   └─ [:, 3]: Dense [1:14]
      ├─ [1]: 0.0
      ├─ [2]: 0.0
      ├─ ⋮
      ├─ [13]: 0.0
      └─ [14]: 0.0

julia> @finch begin
        let m = Finch.chunkmask(5, 1:14)
            for i = _
                for j = _
                    A[j, i] = m[j, i]
                end
            end
        end
    end
NamedTuple()
julia> AsArray(A)
14×3 Tensor{DenseLevel{Int64, DenseLevel{Int64, ElementLevel{0.0, Float64, Int64, Vector{Float64}}}}}:
 1.0  0.0  0.0
 1.0  0.0  0.0
 1.0  0.0  0.0
 1.0  0.0  0.0
 1.0  0.0  0.0
 0.0  1.0  0.0
 0.0  1.0  0.0
 0.0  1.0  0.0
 0.0  1.0  0.0
 0.0  1.0  0.0
 0.0  0.0  1.0
 0.0  0.0  1.0
 0.0  0.0  1.0
 0.0  0.0  1.0

