[ENHANCEMENT] `contract`: add early check for ndims and labels

[ogauthe]

Feature request: better error message when labels1 size does not match array

contract( (1,3,4), ones((1,1)), (1,2), ones((1,1)), (2,3,4))

displays a complicated stacktrace

ERROR: BoundsError: attempt to access Tuple{Base.OneTo{Int64}, Base.OneTo{Int64}} at index [3]
Stacktrace:
  [1] getindex
    @ ./tuple.jl:31 [inlined]
  [2] #10
    @ ~/.julia/packages/TensorAlgebra/zXL7F/src/blockedpermutation.jl:101 [inlined]
  [3] map
    @ ./tuple.jl:356 [inlined]
  [4] #9
    @ ~/.julia/packages/TensorAlgebra/zXL7F/src/blockedpermutation.jl:101 [inlined]
  [5] map
    @ ./tuple.jl:356 [inlined]
  [6] blockpermute
    @ ~/.julia/packages/TensorAlgebra/zXL7F/src/blockedpermutation.jl:101 [inlined]
  [7] output_axes
    @ ~/.julia/packages/TensorAlgebra/zXL7F/src/contract/allocate_output.jl:15 [inlined]
  [8] allocate_output(::typeof(contract), biperm_dest::TensorAlgebra.BlockedPermutation{…}, a1::Matrix{…}, biperm1::TensorAlgebra.BlockedPermutation{…}, a2::Matrix{…}, biperm2::TensorAlgebra.BlockedPermutation{…}, α::Bool)
    @ TensorAlgebra ~/.julia/packages/TensorAlgebra/zXL7F/src/contract/allocate_output.jl:81
  [9] contract(alg::TensorAlgebra.Matricize, biperm_dest::TensorAlgebra.BlockedPermutation{…}, a1::Matrix{…}, biperm1::TensorAlgebra.BlockedPermutation{…}, a2::Matrix{…}, biperm2::TensorAlgebra.BlockedPermutation{…}, α::Bool; kwargs::@Kwargs{})
    @ TensorAlgebra ~/.julia/packages/TensorAlgebra/zXL7F/src/contract/contract.jl:121
 [10] contract(alg::TensorAlgebra.Matricize, biperm_dest::TensorAlgebra.BlockedPermutation{…}, a1::Matrix{…}, biperm1::TensorAlgebra.BlockedPermutation{…}, a2::Matrix{…}, biperm2::TensorAlgebra.BlockedPermutation{…}, α::Bool)
    @ TensorAlgebra ~/.julia/packages/TensorAlgebra/zXL7F/src/contract/contract.jl:111
 [11] contract(alg::TensorAlgebra.Matricize, labels_dest::Tuple{…}, a1::Matrix{…}, labels1::Tuple{…}, a2::Matrix{…}, labels2::Tuple{…}, α::Bool; kwargs::@Kwargs{})
    @ TensorAlgebra ~/.julia/packages/TensorAlgebra/zXL7F/src/contract/contract.jl:92
 [12] contract
    @ ~/.julia/packages/TensorAlgebra/zXL7F/src/contract/contract.jl:81 [inlined]
 [13] #contract#33
    @ ~/.julia/packages/TensorAlgebra/zXL7F/src/contract/contract.jl:62 [inlined]
 [14] contract
    @ ~/.julia/packages/TensorAlgebra/zXL7F/src/contract/contract.jl:52 [inlined]
 [15] contract(labels_dest::Tuple{…}, a1::Matrix{…}, labels1::Tuple{…}, a2::Matrix{…}, labels2::Tuple{…})
    @ TensorAlgebra ~/.julia/packages/TensorAlgebra/zXL7F/src/contract/contract.jl:52
 [16] top-level scope
    @ REPL[126]:1
Some type information was truncated. Use `show(err)` to see complete types.

Adding something like assert ndims(a1) == length(labels1) would make debug easier.

[ogauthe]

fixed by #64